Mass Rapid Transit Authority of Thailand (MRTA) organized Green Office 2021 Project to endorse energy saving and greenhouse gas emission reduction knowledge by organizing MRTA 3R activity (Reuse Reduce Recycle). The activity was conducted by campaigning MRTA executives and officers to sort plastic bottles from other wastes during April – July 2021 to recycle to plastic pellets to make fabric product to give them as souvenir. The result showed that 106,997 bottles (= 1,337.22 Kilograms) were sorted equivalent to a total reduction of 1,162.04 Kilograms Carbon Dioxide-Equivalent. Moreover, there was Green Office Day 2021 Online Activity on Wednesday 22nd September 2021 to disseminate knowledge on energy saving via lecture, educational video and quizzes where 228 people participated in the activity.