Critical professional misconducts among teachers especially at the secondary level of education is a universal challenge that is facing every school in all parts of the world. Based on this realization, the purpose of this paper is to examine the expected roles of teachers, to highlight what constitute teacher?s professional misconducts, to explain the effects or consequences of teachers misconducts and to suggest ways of curbing the teacher?s professional misconducts. It was also gathered that several factors like immoral relationship with female students, increase in examination malpractices, extortion of money from students, poor records keeping, involvement in commercial activities within and outside school were causes of misconducts among teachers in Nigeria. It was also found that poor condition of services, irregular promotion and payment of salaries, poor professional training, societal negative influence, inadequate facilities and instructional supervision were responsible for the misconducts among teachers in Nigeria, the study recommended among other things that thorough screening of candidates being recruited into teaching, regular payment of salary, alleviating poverty of teachers, motivation of teachers and regular supervision and monitoring of teachers.