Soil Transmitted Helminths are group of parasitic nematode worms transmitted to humans by faecally contaminated soil. The majorsoil transmitted helminths parasites to humans are Ascaris lumbricoides, Trichuris trichiura, Necator americanusandAncyclostoma duodenale. Effective prevention and control of STH infections require the identification of local risk factors, particularly among school children. Hence, the aim of this study was to determine the prevalence of STH infections and associated risk factors among primary schools children in Kobo town, Southeast Ethiopia. School based cross- sectional study was conducted from March 2018 to May 2018. Study subjects were selected using systematic random sampling technique. Structured questionnaires were used to gather data on socio-demographic and environmental factors. Stool specimens were collected and examined for parasites using direct wet mount technique. Data were analyzed using SPSS Version 20. The overall prevalence of STH infections in the present study was 26.3%, for at least one STH infection. A total of three STHs species were detected, the most prevalent was Ascaris lumbricoides 81(20.5%), followed by hookworm 15 (3.8%) and Trichuris trichiura 10 (2.5%). In this study the most significantly associated risk factors for the occurrence of STHs were Mother’s educational status, hand washing habit before meal and the place where students defect and dispose their feces (p<0.05). It can be concluded that STH infections, specifically infections due to Ascaris lumbricoides is important problem among the school children of the Kobo town. Therefore, the woreda health office, school community and non-governmental organizations need to give education on personal hygiene, environmental sanitation, and treatment should be taken in to account to reduce the prevalence of the infections. Key words: Kobo town, Prevalence, Risk factors, school-age children, soil transmitted helminth infections,