The aim of this study was to validate a questionnaire on mastery motivation (task and effort) for use with Chinese preschool children in Hong Kong. A parent version and a teacher version were developed and evaluated. Participants included 457 children (230 boys and 227 girls) aged four and five years old, their preschool teachers and their parents. Further, 44 children (39 boys and 5 girls) with developmental disabilities were recruited. The children were assessed on the cognitive sub-test of the Preschool Development Assessment Scale (PDAS). Their parents completed the task and effort motivation scales, as well as the Strengths and Difficulties Questionnaire (SDQ). Their teachers also completed the task and effort motivation scales. Rasch analysis results provided support for the unidimensionality of the parent and teacher versions of the two motivation scales. The parent and teacher versions of the two motivation scales correlated positively with the PDAS cognitive sub-test and the SDQ prosocial scale scores, and negatively with the SDQ total problem behavior scores. Children with developmental disabilities were assigned lower scores by their teachers and parents on the two motivation scales, compared with children with typical development. Reliability (Cronbach's Alpha) of the parent and teacher versions of the two motivation scales were above 0.70. The results suggested that the task and effort motivation scales were promising instruments for the assessment of motivation among Chinese preschool children. (Contains 3 tables and 4 figures.)