Objective: This study examined the efficacy of the Parent and Child Enhancement (PACE) program on child learning, child behavior problems, and parental stress, using randomized controlled trial design, in social services centers. Methods: Eligibility criteria were (1) children aged 2 years at program commencement, (2) low-income, new immigrant, or single-parent families, and (3) parent-child dyads being Hong Kong residents. Intervention group dyads were offered the PACE program (40 two-hour sessions on child learning and parenting). Primary outcomes included child preschool concepts, child behavior problems, and parental stress. Participants were randomly assigned to intervention (76 dyads) and control group (73 dyads) using a random number table, without blinding. Results: Intention-to-treat analysis with 149 dyads indicated improvement in child preschool concepts, decrease in child behavior problems and parental stress in the intervention group, compared with the control group (d = 0.12-0.73). Conclusions: The results provided evidence for the efficacy of the PACE program.