This study was to investigate how mathematical activities with learning together affected young children s ability of mathematical problem-solving. The subjects of this study were 55 five-year-old children. Twenty three children of one class were assigned to the experimental group. Another twenty nine children(in exception of absenteeism and the transfer) were assigned to the control group. For the experimental treatment, the experimental groups were conducted in mathematical learning activities while the control groups were conducted in the free choice activities mathematics manipulation play center. The results of this study showed that mathematical activities with learning together had a positive effects on young children s ability of mathematical problem-solving. Especially, the mathematical activities with learning together had a positive effect highly on young children s sub-category that was classification, pattern, number, measurement, shapes problem-solving.