FORM 6-K



                       SECURITIES AND EXCHANGE COMMISSION
                              Washington D.C. 20549



                            Report of Foreign Issuer



                      Pursuant to Rule 13a-16 or 15d-16 of
                       the Securities Exchange Act of 1934


                    For period ending April 21, 2008

                               GlaxoSmithKline plc
                              (Name of registrant)



               980 Great West Road, Brentford, Middlesex, TW8 9GS
                    (Address of principal executive offices)


             Indicate by check mark whether the registrant files or
                 will file annual reports under cover Form 20-F
                                  or Form 40-F


                              Form 20-F x Form 40-F
                                       --


         Indicate by check mark whether the registrant by furnishing the
        information contained in this Form is also thereby furnishing the
       information to the Commission pursuant to Rule 12g3-2(b) under the
                        Securities Exchange Act of 1934.

                                    Yes No x
                                       --



                      GlaxoSmithKline plc - Block Listing



Application has been made to the UK Listing Authority and the London Stock
Exchange for block listings totalling 20,000,000 Ordinary shares of 25p each to
trade on the London Stock and to be admitted to the Official List upon issuance.
The shares shall rank equally with the existing issued shares of the Company.

The block listings consist of:

10,000,000 Ordinary shares of 25p each under the GlaxoSmithKline Share Option
Plan - ADS.

5,000,000 Ordinary shares of 25p each under the GlaxoSmithKline Share Option
Plan - Ordinary shares.

5,000,000 Ordinary shares of 25p each under the GlaxoSmithKline Savings Related
Share Option Scheme.



S M Bicknell

Company Secretary

21 April 2008.


SIGNATURES


Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorised.



                                                             GlaxoSmithKline plc
                                                                    (Registrant)

Date: April 21, 2008                              By: VICTORIA WHYTE
                                                              ------------------
                                                              Victoria Whyte
                                                 Authorised Signatory for and on
                                                   behalf of GlaxoSmithKline plc