The purpose of this study was to find out the joint and relative contributions ofrnlocus of control, achievement motivation future time orientation, and sex to thernprediction of academic achievement of high school students. Moreover, the studyrnaimed at investigating (1) sex differences in locus of control, achievementrnmotivation, and future time orientation; (ii) the relation of these variables to thernacademic achievements of male and female students; (iii) joint and relativerncontribution of these variables to the prediction of the academic achievement inrneach sex group. The subjects participated in this study were 303 regular (157rnmale and J 46 female) students of high schools in Arsi Region. The method usedrnto sellect the subjects was stratified multi-stage sampling. The instrumentsrnemployed in data collection were Children's Nowicki and Strickland lnternalExternalrnscale (Nowicki & Strickland 1973), achievement motivationrnquestionnaire (Hermans, 1970), and future time orientation scale (Gjesme, J 979).rnAcademic achievement scores of the subjects were secured from rosters. Multiplernregression analysis, t-test, correlation, and correlation difference test werernemployed in the nalysis of the data. Accordingly, the result of multiple regressionrnanalysis indicated that locus of control, achievement motivation, future timernorientation and sex have significant joint contributions to the prediction of highrnschool students' academic achievement. However, further analysis of betarnweights of each variable demonstrated that only sex and future time orientationrnhave significant relative contribution to the prediction of the academicrnachievement of the group. With regard to sex differences in locus of control,rnachievement motivation, and future time orientation, t-test revealed nonsignificantrndifferences between the two sex groups in these variables. Accordingrnto the result of the correlation procedure, locus of control and future timernorientation were significantly related to academic achievement of female students,rnwhile achievement motivation was not. On the other hand, non of the threernvariables was significantly related to the academic achievement of the malerngroup; and hence there was no need of carrying out regression analysis for thisrngroup. As implied by correlation coefficients, correlation difference testrnconfirmed that locus of control and future time orientation were related to thernacademic achievements of female students more strongly than to those of malernstudents. But the strength of relationship between achievement motivation andrnacademic achievement was not significantly different for both sex groups. Thernresult of multiple regression analysis on the data of female students showed thatrnlocus of control, achievement motivation and future time orientation hadrnsignificant joint contribution to the prediction of academic achievement of thisrngroup. Nevertheless, further analysis of beta weights of each variable revealedrnthat only future time orientation has significant relative contribution to thernprediction of the academic performances of this sex group. Discussions andrnconclusions have been made on the basis of these results. Finally" somernimplications were indicated for possible interventions and for further inquiries