Background: The rate of premarital sexual activity, unwanted pregnancies and illegal abortions remain higher among university students. This calls for understanding the knowledge on contraceptive use and sexual behaviours among this high risk group if the incidence of unintended pregnancy, illegal abortions and high sexual risky behaviour are to be minimized. This study aimed to assess ssexual behaviour, contraceptive knowledge and use among female undergraduates' students of Muhimbili and Dar es Salaam Universities in Tanzania. Methods: A cross-sectional analytic study was conducted among undergraduate female students in the two Universities located in Dar es Salaam region, Tanzania. The study period was from June 2013 to October 2013. A self-administered questionnaire was given to 281 students. Of these, 253 were retrieved, giving a response rate of 90%. Data was analyzed using Statistical Package for Social Science (SPSS) for Windows version 17.0. Descriptive statistics were summarized. The chi square test was used to examine relationship between various sociodemographic and sexual behaviours variables with contraceptive use. A P-value of less than 0.05 was considered statistically significant. Results: Results showed that majority (70.4%) of the students have had sexual intercourse. All participants had knowledge of contraception. More than half, 148 (58.5%) of sexually active women reported ever used contraception before while 105 (41.5%) were current contraceptive users. Majority (74.7%) of the sexually active group started sexual activity at young age (19-24 years). Condom, 221(24.3%) and pills, 153 (16.8%) were the known contraceptive methods. The most popular method of contraception used were condoms, withdrawal and periodic abstinence. The main sources of information about contraception were from friends, radio and school (39.5%, 36% and 24%) respectively. Forty (15.8%) women had pregnancies. Of these, 11 (27%) have had unwanted pregnancies among which 54.6% have had induced abortion. Marital status, age at first sex, ever had sex, ever been pregnant and unwanted pregnancies were associated with use of contraception. Conclusions: Most of the student's had knowledge of contraception. However, rate of contraception use is still low. Majority of the respondent were sexually active, with the majority started sexual activity at young age. This needs advocacy for adolescence reproductive health education to promote the use of the available contraceptive services amongst university students.