The purpose of this study was to determine the effectiveness of behavioral and rational emotive behavior therapies (REBT) on conduct disorder among juvenile delinquents. This was a quasi-experimental study design with Kabete Rehabilitation School representing the experimental group and Wamumu Rehabilitation School representing the control group. A total of 94 respondents aged between 13 and 17 years from Kabete and Wamumu rehabilitation schools in Kenya participated in the study (47 for each study arm). A socio-demographic questionnaire was administered, in addition to a selfadministered Child Behavior Checklist (CBCL-YSR) Youth Self Report for ages 11-18 (2001) completed at baseline, midline (3 months post-intervention) and endline (6 months post intervention). CBCL is a standardized tool with a proven validity and reliability of 0.82. The two groups were comparable statistically with respect to key socio-demographic characteristics namely type of facility, age, employment status with the exception of class. Data was analyzed using Statistical Package for the Social Sciences version 20.0 (20). Presentations were done using profile plots and tables. The experimental group showed a steady decline in the mean CD scores over the study period from 19.96 (SD: 5.069) at baseline to mean of 8.26 (SD: 2.625) at endline (p < 0.0001). The control group had a rather staggered decline from mean of 14.94 (SD: 3.953) at baseline to 11.81 (SD: 4.332) at end-line (P > 0.05). Difference-in-differences (DiD) model was used to determine the efficacy of the intervention at post-treatment one and post-treatment two. The DiD estimators at midline was -1.393 (p < 0.0001) and at end-line was -1.204 (p < 0.0001) after controlling for class. The study established a statistically significant reduction of conduct disorder symptoms from a mean of 19.96 at baseline to 8.26 at post-treatment two and this was significant at p<0.001, indicating the effectiveness of behavioral and REBT therapies in treating conduct disorder. Based on the study findings, it is recommended that behavioral and REBT therapies be integrated in the juveniles' rehabilitation program.