This meta-analysis used hierarchical linear modeling to examine 115 single-case studies with 343 participants that examined the effectiveness of social skills interventions for individuals with autism spectrum disorder (ASD). The average effect size of the included studies was 1.40 (SD = 0.43, 95% CL = 1.32-1.48, N = 115). In the further, several common predictors including intervention length, age and gender of the participants, and study quality indicators (provision of sufficient, in-depth, and replicable information of participants, settings/materials, independent variables, and dependent variables) were not found to mediate the intervention effectiveness. Only research design that the study employed was found to impact the intervention effectiveness; the studies using multiple baseline or reversal design had larger effect sizes than studies using other designs. Implications of the results and limitations of this study are discussed.