The purpose of this study is to analyze the relationship of logical thinking skills and integrated process skills, and to investigate the differences in general tendency of subskills by grade level and gender between Korean middle school students and Japanese one. The performance level of skills was measured using GALT and TIPS II. The results are compared with those of Japan (Mattheis et al., 1992). Summary of the results are as follow. 1. Percentages of formal and transitional stage of males are more than females in developmental level. It has been found out that the males attained significantly higher scores of logical thinking skills than the females in middle school stage. The significant differences in scores by gender show a good correlation with those for Japanese middle school students. Developmental level of Korean middle school students shows a remarkable improvement as they move up from 8th grade to 9 one. The significant differences in developmental level by grade also show a good correlation with those for Japanese middle school students. Total scores of GALT for Japanese middle school students are higher than Korean one, but it has been found nearly same scores for 9th grade in both countries. Scores of subskills of logical thinking skills, except correlational reasoning, for Korean students show lower than those for Japanese students. It could be noted that the combinatorial reasoning is considered to be easiest and the correlational reasoning to be most difficult in both countries. 2. It also has been found out similar pattern for integrated process skills in both countries because the males and females did not examplify significant differences, although males gain somewhat higher scores than females in Korea. Scores of subskills of integrated process skills for Japanese middle school students show higher them Korean one. It could be noted that the identifying variables is considered to be easiest and stating hypothesis to be most difficult in both countries. 3. There was a significant relationship (r= .65) between logical thinking skills and integrated process skills, and there were statistically significant differences of the integrated process skills for developmental level. In integrated process skills, the students who belong to the higher grade levels acquired better score than who belong to the lower grade level. It has been also found remarkable improvement between 8th and 9th grade, and there are significant differences for grade level in both countries.