Background: The utilization of STI’s clinic is done to suppress the spread of STIs among the commercial sex workers, men, gays, and the STI's high-risk groups such as public transportation and becak drivers through the health services implemented at STI’s clinic. Aims: analyze the relationship between sociodemographic (age, education, tribe, occupation and the distance the venue of service facility) and the behavior of public transportation and becak drivers and the utilization of STI’s clinic. Methods: This quantitative survey study with a cross-sectional design was conducted from December 2013 to May 2014. The population of this study was all of the STI's high-risk groups with high mobility and knew about the existence of STI's clinic at Puskesmas Tomuan. They were 62 public transportation and becak drivers hanging out in the working area of Puskesmas Tomuan, Pematang Siantar selected through consecutive sampling technique. The data obtained were analyzed through univariate analysis. Chi-square test and multiple logistic regression tests. Results: The result of this study showed that only 19 respondents (30,65%) utilized the STI's clinic. There was a relationship between education (p<0,001), occupation (p = 0,003), and behavior (p < 0,001) with the utilization of STI’s clinic at Puskesmas Tomuan. The most influential variable on the utilization of STI's clinic at Puskesmas Tomuan was education with the value of coefficient B= 10,335. Conclusion: Pematang Siantar Office Health Service is suggested to improve the knowledge of the high- risk group especially the public transportation and becak drivers with a low educational background who was susceptible to STI's disease through the extension on STI’s disease and the utilization of STI’s clinic.