Attempts to reduce the decline in physical activity (PA) in adolescence have been the focus of many public health interventions. This study aimed to (1) determine differences in moderate-to-vigorous PA (MVPA) levels between weekdays and weekends and (2) identify adolescents meeting current PA guidelines (PAG). To meet these objectives, 186 Thai adolescents aged 13 to 18 years were asked to wear an ActiGraph accelerometer for 7 consecutive days. The results showed that MVPA levels were significantly higher in boys than girls on both weekdays (P < .01) and weekends (P < .05). MVPA was higher during weekdays compared with weekend days. Additionally, MVPA levels tend to decline with increasing age during adolescence. The results also showed statistically significant differences between genders in the proportion of adherence to PAG for youth. This study highlights the need to take weekend-weekday differences into account when developing PA interventions for adolescents.