This study was conducted to compare effects of concept mapping and conceptual change texts instruction over traditional instruction on 10th grade students' understanding of acid and base concepts. 110 students from 6 classes of a chemistry course taught by the same teacher were enrolled in the study. There were four experimental group classes and two control group classes. Two experimental groups class were instructed with concept mapping instruction; and the other two experimental groups were taught with conceptual change texts instruction and the next two classes were assigned as control group students instructed with traditional instruction. All students were administered the Acids and Bases Concept pre-test and post-test. A two-way ANOVA was used for statistical analyses. The results showed that concept mapping instruction and the conceptual change texts instruction caused a significantly better acquisition of scientific conceptions related to acids and bases than the traditional instruction. Also, there was no effect of gender difference on understanding of acid and base concepts. (Contains 37 references.) (Author/MM)