This study investigated the direct relationship between home play opportunity and prospective school readiness, and the indirect relationships as mediated through object and social mastery motivation among Hong Kong Chinese kindergarten children. Participants were 106 local children (44.4% girls, mean age = 60.0 months) and their parents and teachers. Parents reported the demographic information and children's home play opportunity at time 1 (beginning of the school year), whereas children's object mastery motivation, social mastery motivation, and school readiness were reported by their teachers at time 2 (six months later). Research Findings: Results from the path analytic model revealed that children's home play opportunity significantly predicted their object mastery motivation, but not social mastery motivation or school readiness. Both object and social mastery motivation were positively associated with school readiness. Furthermore, the indirect relationship between home play opportunity, object mastery motivation, and school readiness was significant, but the one via social mastery motivation was non-significant. Practice or Policy: The findings highlight the collective roles of object and social mastery motivation in predicting children's school readiness. The results also suggest the desirability of providing kindergarten children with a varied and accessible home play environment which may promote their mastery motivation and school readiness.