The main purpose of this study was to investigate the effects of the teaching assistant on mathematical remedial instruction. A quasi-experimental design was used in the study. The subjects were first-grade students in a junior college. The experimental group was treated with mathematical remedial instruction, while the control group was treated with nothing. The midterm was assigned as pretest and the final exam was assigned as posttest. The methods applied to analysis by SPSS21.0 were descriptive statistics, t-test, one-way ANOVA, one-way ANCOVA and Scheffé Method. The result of this study indicated that the teaching assistant was helpful to mathematical remedial instruction. It is hoped that the finding of the research can provide researchers' references.