The purpose of this study was to examine the differences of young children s mathematical problem solving ability between experimental and comparative groups, when spatial visualization activities with teacher s intervention was applied to the experimental group. Two instruments had been used in this study. First, Pictorial Test of Intelligence for Children(PTI) was used for testing group s homogeneity. PTI was Korean version of French s(1964) Pictorial Test of Intelligence(Seo, Jeong, & Choi, 1985). Secondly, Problem Solving Ability Test was used for pre- and post-tests. This instrument was originally constructed by Ward(1993) and then translated into Korean by Hwang(1996). The results of this study were as follows: 1. Teacher s intervention applied to the experimental group enhanced the ability of young children s mathematical problem solving of spatial visualization activities then comparative group(p<.01). 1-1. Recognition of similarity difference in mathematical problem solving ability sub-factors showed statistically not significant difference between two groups. 1-2 Classification in mathematical problem solving ability sub-factors showed statistically significant difference between two group(p<.01). 1-3. Patterning in mathematical problem solving ability sub-factors showed statistically not significant difference between two groups. 1-4. Measurement in mathematical problem solving ability sub-factors showed statistically not significant difference between two groups.