We have made payments with cash or credit cards. But since Kakao Pay was launched in 2014, mobile payment for online and off-line transactions is growing very rapidly. Interestingly, most major mobile payment services in Korea or overseas were designed to augment the companies’ primary businesses. For example, Kakao Talk and Facebook started their payment services, Kakao Pay and Facebook Pay, to improve user convenience. However, prior research has paid little attention to the relation between primary business and mobile payment service. Focusing on Kakao, the current research investigates whether the gratifications of five motivations(entertainment, socializing, information, conformity, practicality) to use Kakao Talk affect the continuous usage intention of Kakao Pay. In addition, we test the moderating effect of age(2030 vs. 4050 vs. 60 or older). We analyzed the data of 478 respondents and found that the gratifications of entertainment, socializing, and practicality of Kakao Talk increased significantly the continuous usage intention of Kakao Pay. However, these results were different by age group. Socializing, information and practicality for 2030, entertainment and practicality for 4050, and entertainment and socializing for 60 or older were positively significant factors affecting the continuous usage intention of Kakao Pay.