Vasak I Mamikonian (died c. 367) was an Armenian military officer from the Mamikonian family, who occupied the hereditary office of sparapet (generalissimo) of the Kingdom of Armenia under the Arsacid king Arshak II (reigned c. 350–367/8). According to the Buzandaran Patmut‘iwnk‘, which may have been composed c. 470, Vasak was known for playing a disruptive role between Arshak II and the Sasanian monarch Shapur II (r. 309–379), and for orchestrating many Armenian victories over the Sasanian army. Vasak was put to death in c. 367 by Shapur following the capture of Arshak.