Many Taiwan companies have plants in Vietnam. Vietnam is an important economic partner of Taiwan. To service customers, banks must have services in both Taiwan and Vietnam. Restated, banks must find ways to effectively promote mobile banking services to Taiwan and Vietnam customers. However, the adoption of mobile banking has increased gradually in Taiwan, but banks in Vietnam have difficulties to apply services actually. As the security of phone banking is the customer’s primary concern, customers may accept unfamiliar technology via subjective norm. To understand how subjective norm affects customer acceptance, this study examines mobile-banking adoption in Taiwan and Vietnam in terms of the effects of subjective norm, performance expectancy, effort expectancy, facilitating conditions, and attitude toward and intention to adoption mobile banking services. Models were compared using data collected from 440 Vietnamese and 372 Taiwanese respondents. Analytical results reveal that subjective norm and facilitating conditions explain differences in adoption between Taiwan and Vietnam. Subjective norm affects positively effort expectancy, performance expectancy, and facilitating conditions in Taiwan and Vietnam. Subjective norm also positively affects attitude toward and intention to adopt mobile banking services in Vietnam, but not in Taiwan. Facilitating conditions affect attitude positively, but not affect intention positively in Taiwan. Facilitating conditions positively affect attitude toward and intention to use mobile banking services positively in Vietnam. Finally, managerial implications for banks, based on findings, are given.