INTRODUCTION Soil transmitted helminths are wide spread in developing countries and in Ethiopia the prevalence of STHs varies in different parts of the country. The aim of this study was to determine the prevalence and intensity of soil transmitted helminths among school children of Mendera Elementary School Jimma town, Southwestern Ethiopia. METHODS A cross-sectional study was conducted between March 29 and April 9, 2010 to determine the prevalence and intensity of soil transmitted helminths among elementary school children. The study participants were randomly selected from class enrollment list after proportional allocation of the total sample size to each grade. Data about the background characteristics were collected using structured questionnaire. The stool samples were examined by McMaster method for the egg count which was used to determine intensity of infection. Data were analyzed using SPSS for windows version 16 and p-value less than 5% was considered as statistically significant. RESULTS Of the total 715 stool specimens examined, 346 were positive for at least one intestinal parasite making the prevalence 48.4%. The most prevalent parasites were Ascaris lumbricoides 169 (23.6%) and Trichuris trichiura 165 (23.1%). The prevalence of soil transmitted helminth in this study was 45.6% (326/715). There was statistically significant difference in the prevalence of Trichuriasis between those who use latrine always and who use sometimes (p = 0.010). Females are two times more likely to be positive for Ascaris than males (p = 0.039). Majority of the students had light infection of soil transmitted helminths and none of them had heavy intensity of infection of Trichuriasis and hookworms. CONCLUSION Nearly half of the school children were infected with at least one STHs and majority of the students had light infection of soil transmitted helminths. Students who did not wash their hands after defecation were three times more likely to be positive for Ascaris infection than those who washed their hands after defecation. Therefore, measures like health information dissemination on the advantage of washing hands after defecation and on proper use of latrine should be taken into account to alleviate the problem.