Purpose: This study was to define the significant difference of knowledge and attitude of sex according to general demographics in undergraduate students. Method: The data was collected from 101 undergraduate students from May to June 2014. The data collection was done by structural survey in the from of questionnaire. The collected data's demographic and descriptive was process using SPSS Statistics(version 18.0 for Windows). Results: There was statistically significant difference in knowledge of sex according to sex(t=-3.354, p<.01), grade(t=12.992, p=<.001), dating experience (t=3.547, p<.05). But there was not statistically significant difference in attitude of sex. Therefore we should develop the program to improve knowledge and attitude of sex according to general demographics in undergraduate students.