Sex education is out of bounds in a typical African society due to cultural values and belief systems. So, sex education is assumed to support promiscuity among adolescents. Premised on this, teachers equally have lopsided views of responsibility. This greatly has hampered the success of inculcation of sex education in high school curriculum and the teaching of the subject. This study aimed to assess the perception of high school teachers towards the contents and timing of sex education in secondary schools in Ile-Ife, South-West Nigeria. 200 high school teachers were randomly selected and served questionnaire that has been pretested and standardized for data collection. Data collected was analyzed using descriptive statistics. Teachers' responses showed positive attitude towards sex education and its inclusion into secondary school curriculum. Higher numbers of the respondents were of the opinion that it is best suited for Secondary schools. However, there were discrepancies as regard the appropriate age at which students should be taught sex education. Also, there were variants on the contents of sex education curriculum. One-third of the teachers indicated that 16 to 18 years were appropriate for sex education. Foremost among the factors identified affecting introduction of sex education into school curriculum were culture, religion, mass media and peer influence. The study concluded that appropriate age, timing and class are major factors to be considered before the introduction of sex education into secondary school curriculum.