The main purpose of this study was to examine the child´s behavior of categorization in relation with their sccio-economic level and age. One hundred and twenty 1st, 3rd and 5th grade children in primary schools were selected as subjects. The instruments used in this study were thirty-two color pictures. Each child was asked to choose the pictures were alike in some way, and to tell on what basis the pictures were selected. Two methods were used in scoring the child´s responses: 1) content analysis-the responses was classified into four different attributes, global-descriptive, analytic-descriptive, relational and inferential, based on which the child grouped the objects; 2) structure analysis-the responses were classified into three grouping structures, superodinate, complexive and thematic. The results of this study were as follows: 1) The children´s behavior of categorization was closely related to age and socio-economic level. 2) Inferential and analytic-descriptive attributes used in grouping showed an increasing tendency with age, whereas relational and global-descriptive attributes showed a decreasing tendency. 3) Superordiante grouping structure showed an increasing tendency with age; whereas complexive showed a decreasing tendency. 4) The children from higher socio-economic level reflected more superordinate grouping structure but less complexive than those from lower socio-economic level. 5) The children from higher socio-economic level reflected more inferential and analytic-descriptive attributes as the basis of grouping but less global-descriptive and relational than those from lower socio-economic level.