This research aims to describe about proportional reasoning of seventh grade students of Junior High School in resolving the comparison problem reviewed from mathematics ability and sex. This study is qualitative research. Students' proportional reasoning in resolving the comparison problem in this research will be identified based on indicators of proportional reasoning namely understanding the covariation,  knowing the difference between the correlation of proportional and non - proportional,  applying strategy in proportional and non -  proportional correlation,  and identifying the different correlation between quantities. The first research process is compiling test of mathematics ability which consist of five questions of National Examination which are converted into description questions. The second,  compiling task of comparison questions,  and the third is compiling interview guidelines.  The result of the study shows that between male and female students with equal ability in each mathematics group (high and medium) in proportional reasoning are almost the same.  The male students with high and medium ability are different in knowing the difference between proportional and non - proportional correlation namely in seeking the correlation between quantities, are different in applying settlement strategy, and in finding the different correlation between quantities.  Whereas,  the female students with high and medium ability are different in knowing the difference between proportional and non - proportional correlation namely in seeking pattern of correlation between quantities.