Background: Children with autism spectrum disorder (ASD) often exhibit deficits in pretend play and have less playfulness. The purpose of this study was to evaluate the relationship between pretend play and playfulness in children with autism spectrum disorder, while controlling for severity of autism behaviors, verbal comprehension, and age. Methods: A sample of 72 children with ASD aged between 3 and 12 years were assessed with the Child-Initiated Pretend Play Assessment, Test of Playfulness, and Childhood Autism Rating Scale, respectively, for their pretend play, playfulness, and severity of autism behaviors. Correlation and multiple regression analyses were conducted. Results: The results of Pearson correlation coefficients revealed that the pretend play variables had mild to moderate associations with the playfulness variables (r = −0.25 to 0.68). The multiple regression analyses showed that, overall, the internal locus of control was the significant predictor of the pretend play variables (accounting for 5-47% of the variance, p < 0.001). The six pretend play variables were all important predictors of all playfulness variables (explaining 41-76% of the variance, p < 0.001-0.047). Particularly, the elaborate pretend play action was a significant predictor of all four playfulness variables. Our findings indicated that the more children with ASD engaged in pretend play, the more they experienced playfulness. Conclusion: Clinicians could help children with ASD improve their feeling of being in charge of their play in order to develop better performance in pretend play. Assisting children with ASD to engage in pretend play is important to promote their internal experience of playfulness.