This study examined condom use intentions among adolescent boys in relation to the constructs of the Theory of Planned Behavior (TPB): attitude toward the behavior (ATB), subjective norm (SN), and perceived behavioral control (PBC). The potential moderating effects of sexual orientation and gender characteristic (masculine/feminine) were also explored. Anonymous survey data were collected from 929 students enrolled in a boys' senior high school in Taiwan (response rate: 89.9%). Multivariate logistic regression analyses found higher condom use intentions linked to more positive ATB (adjusted odds ratio [AOR] = 8.09) and supportive SN (AOR = 2.73), as well as high PBC under facilitating conditions (AOR = 2.04). Notably, nonheterosexual boys perceiving supportive SN (AOR = 0.23) or high support for condom use from teachers and health educators (AOR = 0.10 and 0.26, respectively) had lower condom use intentions than their heterosexual peers. By contrast, relatively feminine boys perceiving supportive SN (AOR = 2.06) or high support from close friends (AOR = 2.18) had higher condom use intentions than their masculine counterparts. In conclusion, ATB and SN were strongly linked to condom use intentions; PBC was significant only under facilitating conditions. Sexual orientation and gender characteristic had important moderating effects. These empirical findings could inform tailored health education programs to increase condom use intentions in the male student population.