In order to analyze the effect of a newly developed video teaching aid in learning, the teaching aid, $quot;Practice in Genetic Engineering$quot; (Choi and Ahn, 1991), was applied in classroom teaching in a general high school and a science high school in Seoul district. Experimental groups were taught using the video teaching aid, and control groups were taught in lecture style. The achievements of student in learning gene recombination and generation of monoclonal antibodies were compared between the two groups after the equalization of the initial gap that occurred in the practical lecture before using this video teaching aid. In the result of covariance analysis, there was statistically meaningful difference(P$lt;0.01) between experimental group and control group in both high schools. Thus, lecture using this video teaching aid proved to be effective. Effect of the video teaching between science high school and general high school also showed statistically meaningful difference(P$lt;0.05). However, there was not significant difference among the achievement groups within the general high school. In post-lecture questionnaire of 153 students, 91.6% of students answered that the video teaching aid was helpful for the understanding of genetic engineering. Over 94% of 34 biology teachers answered that the teaching aid might be very helpful for the students, and that they would use the video in practical teaching. From this study, we conclude that $quot;Practice in Genetic Engineering$quot; which was made to cope with the biology curriculum of high school in Korea is a useful video teaching aid for the study of genetic engineering that is one of the most difficult subject in learning and teaching.