Purpose: This intervention compares the effectiveness of daily step count targets with time-based prescription for increasing the health-related physical activity of low-active adolescent girls. Methods: We assigned participants (N = 85, mean age 15.8 + 0.8 yr) depending on school attended to a control (CON), pedometer (PED), or minutes (MIN) group. The intervention groups were involved in a 12-wk physical activity self-monitoring and educative program. The only difference between the intervention groups was that the PED group set daily step count targets whereas the MIN group set daily time-based goals for physical activity involvement. Pre-, mid-, and postintervention changes in physical activity (4-d blinded step count and 3-d physical activity recall) and body mass index (BMI) were assessed using a series of 3 (group assignment) x 3 (time) ANOVA. Where significant interactions were found, separate follow-up simple main effects tests were used. Results: At postintervention, only the PED group had significantly increased their total activity as measured by a 4-d step count, when compared with the control (P = 0.03, ES = 0.13). The group, time, and interaction effects for 4-d step count were significant, indicating that although both the participants in the PED and the MIN groups significantly increased their step count across the 12-wk intervention (P = 0.00-0.01), the participants in the PED group had a greater increase at the midintervention time point (P = 0.04, ES = 0.10). No pre-, mid-, or postintervention changes were reported in any group for BMI (F = 1.18, P = 0.32). Conclusion: The use of pedometers and daily step count targets with low-active adolescent girls may result in short-term (6 wk) enhanced physical activity related outcomes when compared with traditional time-based physical activity prescriptions. However, both interventions appear to result in similar improvements in physical activity when duration of the observation is extended to 12 wk.