Press release
May 10, 2018

Notice of Stock Split and Partial Amendment to Articles of Incorporation

Tokyo, Japan and London, UK, 10 May 2018 – Sosei Group Corporation (“Sosei” or the “Company”; TSE Mothers Index: 4565), the world leader in GPCR medicine design and development, announced that at a meeting of the Board of Directors held today, it resolved to conduct a stock split and partially revise the Articles of Incorporation.

1. Purpose of the Stock Split
   1.1. To improve the liquidity by reducing the amount per trading unit of investment in Sosei shares.
2. Overview of the Stock Split
    2.1. Method of Stock Split The record date of the stock split will be 30 June 2018 (as the record date falls on a Saturday, the actual date shall be Friday 29 June 2018). Each              share of common stock owned by shareholders recorded on the last Register of Shareholders as of record date will be split into four shares.
    2.2. Number of Shares to be Increased by the Stock Split
           2.2.1. Total number of issued shares before stock split: 19,054,984 shares
           2.2.2. Number of shares to be increased by this stock split: 57,164,952 shares
           2.2.3. Total number of shares outstanding after stock split: 76,219,936 shares
           2.2.4. Total number of authorized shares after stock split: 149,376,000 shares
           Note: The total number of issued shares is as of 10 May 2018, and does not include any increase in the number of issued shares that could occur as a result of the                      exercise of stock acquisition rights.


    2.3. Adjustment of Exercise Price of Stock Option In connection with the announced stock split, the exercise price of stock acquisition rights shall be adjusted as follows after              the record date.

3. Stock Split Schedule
    3.1. Date of announcement of the record date: 14 June 2018
    3.2. Record date: 30 June 2018 (Saturday)
    3.3. Effective date: 1 July 2018 (Sunday)
4. Change in the Amount of Stated Capital
    4.1. There is no change in the amount of stated capital with respect to the stock split.
5. Partial Amendment to the Articles of Incorporation
    5.1. Purpose of the Amendment Accompanying the stock split, Sosei shall partially revise its Articles of Incorporation to take effect on 1 July 2018 (Sunday) pursuant to Article            184, Paragraph 2 of the Companies Act.

    5.2. Content of the Amendment Article 5 of the current Articles of Incorporation shall be changed to increase the total number of authorized shares in proportion to the stock                split ratio.