The purpose of this study was to assess the determinants of teachers participation in co-curricular activities in Nefa silk lafto sub city secondary schools. To this end, a descriptive survey design was employed, in which both qualitative and quantitative techniques were applied. In the study 3 sample groups encompassing, 324 students, 129 teachers and 28 principals participated. Questionnaire, interview and observation checklist were instruments used to collect data. After data were collected, analysis was made qualitatively and quantitatively. Hence, the results suggested that majority of participants had good awareness on the co-curricular activities. Moreover, the analyses confirmed that grade level and sex significantly affected the participation of students in co-curricular activities. Additionally; it was found that the co-curricular activities were not properly organized in the schools. Regarding factors that negatively affect the practical participation of co-curricular activities, the major were: lack of budget and material, low motivation of teachers, absence of facilities, low interest of teachers and absence of supportive material for teachers and work load of teachers. Hence the study concludes that the participation of teachers in co-curricular activities were not good. The study suggested that: trainings for teachers and principals, use of incentives to motivate teachers, systematically organize co-curricular activities to attract the teachers, using income generating scheme to reduce constraints of budget. Finally, in order to create competitive atmosphere among participants the establishment of effective continuous monitoring and evaluation mechanism need to be established.