The purpose of this study was to investigate the mathematical proof ability among ninth grade students in Muscat region and its relationship to their mathematical logical thinking, and also to investigate the differences in their levels of mathematical logical thinking (high, average, low), sex, and levels of mathematical proof skills (translation, derivation, construction, evaluation). The sample consisted of (321) subjects, (162) males and (159) females from six school in Muscat region. All subjects were administered into mathematical proof test developed by the researcher and mathematical logical thinking test. The findings showed that: - The average of students' performance on mathematical proof test is lower than the educational accepted criterion. - There was a positive relationship between mathematical proof and mathematical logical thinking. There were significant differences in student's mathematical ability proof due to their levels of mathematical logical thinking. - There was no significant difference between male and female student's in mathematical proof ability. - There were significant differences in student's mathematical ability proof due to their levels of mathematical proof skills. Eventually, the study recommended helping students to develop their mathematical proof skills by developing facility with inductive and deductive reasoning.