Director/PDMR Shareholding

Mereo BioPharma Group plc

 ("Mereo" or the "Company")

Notification of PCA Dealing

London, 27 December 2018 - Mereo BioPharma Group plc (AIM: MPH), a clinical stage UK based biopharmaceutical company focused on rare diseases, received notification that on 21 December 2018, Eric Scots-Knight, a person closely associated (PCA) with Denise Scots-Knight, Chief Executive Officer of Mereo, purchased ordinary shares of £0.003 each in the Company, as set out in the following table.

The below announcement and notification is made in accordance with the EU Market Abuse Regulation. The form required under the EU Market Abuse Regulation follows.

DEALING NOTIFICATION FORMFOR USE BY PERSONS DISCHARGING MANAGERIAL RESPONSIBILITY AND THEIR CLOSELY ASSOCIATED PERSONS

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About Mereo

Mereo is a biopharmaceutical company focused on the development and commercialization of innovative therapeutics that aim to improve outcomes for patients with rare diseases. Mereo's strategy is to selectively acquire product candidates that have already received significant investment from pharmaceutical companies and that have substantial preclinical, clinical and manufacturing data packages. In December 2018, Mereo announced the proposed combination of Mereo and OncoMed Pharmaceuticals, with the transaction expected to close in the first half of 2019. Each of Mereo's four product candidates has previously generated positive clinical data for Mereo's target indication or in a related indication. Since inception Mereo has commenced large, randomized, placebo-controlled Phase 2 clinical trials for all four of the product candidates:

· BPS-804 for osteogenesis imperfecta (OI). The Company recently announced completion of enrolment with 112 adult patients in a Phase 2b dose ranging study with some initial data expected in the H1 2019 and top-line dose ranging data in late 2019. A pediatric Phase 3 study design has also been approved by the EMA. BPS-804 has orphan designation in the US and EU and has been accepted into the PRIME and Adaptive Pathways in EU;

· MPH-966 for alpha-1 antitrypsin deficiency (AATD). The Company recently announced first patient in in a Phase 2 dose ranging study in the US with data expected in late 2019;

· BCT-197 for acute exacerbations of COPD (AECOPD). The Company announced positive top-line Phase 2 data in December 2017; and

· BGS-649 for hypogonadotropic hypogonadism (HH). The Company announced positive top-line Phase 2b data in March 2018 and positive results in December 2018 from the safety extension to the Phase 2b clinical trial.

· As at September 30, 2018 Mereo had (unaudited) total cash resources of approximately US$44.6 million