Syrian War has caused destruction and misery specially for the Syrian people who became the party who got affected directly. During the war that is still on going since 2011, almost 500.000 people have been killed where thousands amongst it were victims of the use of chemical weapons by the regime of Bashar al-Assad since 2012. Many party has been involved in Syrian War including the United Kingdom. As a nation, The United Kingdom have already involved in Syrian War but only in terms of humanitarian assistance. The United Kingdom then decided to release a new foreign policy to do a military attack on Syria’s chemical weapon stockpile. In order to see the reason why the United Kingdom is involving itself militarily in the Syrian War, the writer use English School ‘International Community’, National Interest, and Foreign Decision Making process as intruments of analysis in this research. Any results from this research of why did the United Kingdom involving itself militarily in Syrian War is that the United Kingdom wanted to detterent the capability of Syria’s chemical weapons with the justification of the doctrin to protect (Responsibility to Protect/R2P) its national security, global world, and to avoid the use of chemical weapons in the future.