Massively multi-player online games (MMOGs) have been one of the fastest growing online entertainments and have attracted a great sum of venture investment. Yet, little empirical research has been conducted to examine the interrelationships between gamers' motivations and their post-adoption behaviors. This study aims to explain gamers' continuance intention to play MMOGs by integrating motivations for playing MMOGs into the information systems (IS) continuance model. The authors conducted an online survey of 392 World of Warcraft gamers and validated the model with structural equation modeling. With the majority of hypotheses being substantiated, the results revealed that the extended IS continuance model demonstrates the satisfactory explanatory power of gamers' continuance intention to play MMOGs. It was shown that achievement and immersion motivations positively associate with enjoyment and that enjoyment and satisfaction jointly predict the continuance intention to play MMOGs. The study also discusses theoretical and practical implications.