Introduction Adolescent obesity is one of the most serious global public health challenges. Social networking sites are currently popular among adolescents. Therefore, the obesity prevention program for Korean American adolescents was developed on the most popular social networking site, Facebook. The purpose of this study was to evaluate the usability of a culturally tailored Facebook-based obesity prevention program for Korean American adolescents (Healthy Teens). Method An explorative descriptive design of usability testing was used. Usability testing employing one-on-one observation, the think-aloud method, audio taping, screen activity capture, and surveys was performed. Twenty participants were recruited from two Korean language schools (mean age, 15.40 ± 1.50 years). Recruitment and user testing was performed between February and April 2014. Content analysis, using the inductive coding approach, was performed by three coders to analyze transcriptions. Descriptive statistics were used to analyze quantitative data including demographic characteristics, perceived usability, eHealth literacy, and health behaviors. Results Testing revealed several usability issues in content, appearance, and navigation. Participants' comments regarding content were positive. Although the Facebook platform provided limited flexibility with respect to building the site, participants described the program's appearance as appropriate. Most participants did not experience difficulty in navigating the program. Discussion Our preliminary findings indicated that participants perceived the Healthy Teens program as usable and useful. This program could be used as a robust platform for the delivery of health education to adolescents. Further research is required to assess the effects of Facebook-based programs on adolescent obesity prevention.