The purpose of this study was to examine the effects on science achievement and science-related attitude by teaching strategy which includes STS materials in biology classes. The subjects consisted of 205 students at 10th grades who were enrolled in a high school of commerce. The subjects were divided into 2 experimental groups and 2 control groups. Experimental groups were taught by the STS strategy including the 4 STS materials. Teaching strategy at control groups did not include STS materials. The STS materials were related with the topic of `cell devision`, `reproduction` and `development` which were included at current Korean high school biology textbooks. The results of this study can be summarized as follows: 1. Students at the experimental groups showed higher science achievement than those at the control groups(p$lt;.01). 2. Students at the experimental groups showed more positive science-related attitude than do those at the. control groups(p$lt;.001). In particular, at the domain of `science class`(p$lt;.01). `science class content`(p$lt;.01), and `infusing STS content`(p$lt;.001), students at the experimental groups showed higher positive attitude.