SecProbe.io

Mail Stop 4720

September 1 8, 2017

José G.  Cantera
Chief Financial Officer
Banco Santander, S.A.
Ciudad Grupo Santander
28660 Boadilla del Monte
Madrid, Spain

Re: Banco Santander, S.A.
 Form 20-F for the Fiscal Year Ended December 31, 2016
Filed March 31 , 2017
Form 6 -K Filed August 1 , 2017
File No . 001 -12518

Dear Mr. Cantera :

We have reviewed your filings and have the following comments.  In some of our
comments, we may ask you to provide us with information so we may better understand your
disclosure.

Please respond to these comments within ten business days by providing the requested
information or advise us as soon as possible when you will respond.  If you do not believe our
comments app ly to your facts and circumstances, please tell us why in your response.

After reviewing your response to these comments, we may have additional comments.

Form 20 -F for the Fiscal Year Ended December 31, 2016

Item 4 .B.  Business Overview,  page 39

1. We note you frequently disclose changes in financial metrics excluding the exchange rate
impact on a geographic basis, regional basis, segment basis, and occasionally on a
consolidated basis.  Please respond to the following to help us better und erstand how the
calculations are performed for this disclosure:

 Tell us in detail how you calculate the changes in financial metrics excluding the
exchange rate impact.

José G.  Cantera
Banco Santander, S.A.
September 1 8, 2017
Page 2

  Provide us the supporting quantitative details for financial metrics disclosed in t he 5th
paragraph for Brazil on page 44 and the 4th paragraph for Mexico on page 45 (e.g.
profit attributable to the Parent, total income, etc.) including and excluding the
exchange rate impact and provide any supporting commentary needed to fully
understand the source of the amounts and the basis for the calculations.

 Provide us the supporting quantitative details for the calculation of the profit
attributable to the Parent bank from Latin America, excluding the exchange rate
impact, which is disc losed on page 44.  Please ensure your response clearly indicates
whether certain countries are excluded from this calculation.

 Provide us the supporting quantitative details for the calculation of Global
Transaction Banking profit attributable to the Pare nt, excluding the exchange rate
impact, disclosed on page 48.  As part of your response, please tell us all the countries
that contribute to this unit, and indicat e if any countries are excluded  from the
calculation.

 Provide us the supporting quantitative  details for the calculation of consolidated
administrative expenses, excluding the exchange rate impact, which is disclosed on
page 115.   Please ensure your response clearly indicates whether certain countries are
excluded from this calculation .

Results of Operation for Santander, page 109

2. We note your disclosure of the metric “cost of credit” throughout your filing on both a
consolidated and segment basis.  Please tell us, and revise future filings to disclose, how
cost of credit is calculated.

Form 6 -K Filed August 1, 2017

General

3. We note on your earnings call for the half year 2017 results held on July 28, 2017, you
discussed the expected impact of IFRS 9 in response to an analyst question.  Specifically,
your CFO noted that you expect the impact of  IFRS 9 to be approximately 15 basis
points, and that the acquisition of Banco Popular may increase that estimate by 4 or 5
basis points, for a total possible impact in the region of 20 basis points.  Please respond to
the following:

 Please clarify for us  which line item or capital metric you expect to be impacted.

 Please tell us whether you plan to provide updated disclosure regarding IFRS 9 in
your June 30, 2017 financial statements prepared in accordance with IAS 34.  If so,

José G.  Cantera
Banco Santander, S.A.
September 1 8, 2017
Page 3

 please tell us whether you plan to provide any quantitative information regarding the
expected impact upon adoption.  If not, please tell us why.

We remind you that the company and its management are responsible for the accuracy
and adequacy of their disclosures, notwithstanding an y review, comments, action or absence of
action by the staff.

You may contact Michael Volley, Staff Accountant, at 202-551-3437  or me at 202-551-
3512 with any questions.

Sincerely,

/s/ Stephanie L. Sullivan

 Stephanie L. Sullivan
Senior Technical and Policy Advisor
Office  of Financial Services