The purpose of the present study was to compare the effectiveness of context based instruction over teacher centered chemistry instruction on 9th grade students' understanding of cleaning agents topic and their attitudes toward environment. Moreover students' science process skills were measured for using as a covariate. Participants were 222 ninth grade students from eight classes. Experimental group students were instructed with context based instruction and control group students were instructed with teacher centered chemistry instruction through five weeks. Cleaning Agents Achievement Test and Attitudes toward Environment Scale were used as pre and post tests. Science Process Skills test was used only as a pretest. According to statistical analyses (MANCOVA), there was a significant mean difference with respect to cleaning agents topic between the experimental and control group in the favor of experimental group and no significant difference with respect to attitude toward environment between the groups. Beside, science process skills were a strong predictor for understanding the cleaning agents topic.