The present study was carried out to examine the impact of computer-assisted mathematics instruction on improving the math attitude of ninth grade girls. This quasi-experimental research had a pretest-posttest control group design. The statistical population of the study comprised all ninth grade girls in academic year 2015-2016 in Hashtgerd (N= 4141). The sample included 50 ninth graders who were selected through random multi-stage cluster sampling method and randomly assigned to experimental (N= 25) and control (N= 25) groups. The instrument consisted of Aiken Mathematics Attitude Scale (1971) which was revised by Yushau (2011). Cronbach’s alpha coefficients for the reliability of the measure were 0.85 in the present study and 0.81 in the research undertaken by Zaki (2014). The Mathematics Attitude Scale was administered to both experimental and control groups as the pretest. In the next step, the experimental group was subjected to the experimental variable (computer-aided mathematics instruction) for 16 sessions. Afterwards, the posttest was given to both groups. Results of covariance analysis showed that there was a significant relationship between computer-assisted mathematics instruction and students’ attitude toward math. In fact, computer-assisted mathematics instruction improves ninth graders’ attitude towards mathematics.