The purpose of the study was to determine the relationship between teachers’ attitude towards teaching HIV/AIDS education and students’ knowledge and attitude towards sexual behaviour in secondary schools in the Coast Region of Kenya. The study used descriptive survey research design. The samples comprised 421 respondents of which 33 were teachers and 388 students in 13 secondary schools. Questionnaires and interview schedule were used to collect the data. The validity of the instruments was checked by the supervisors and other experts in the field of research. Reliability coefficients of the instruments were 0.8 for both teachers and students’ questionnaires. The descriptive statistics that were used were frequencies and percentage. Chi-squire statistics was used to test the hypotheses in the study. The hypotheses testing was done at α = .05 level of significance. The data collected in this study was analysed using Statistical Package for Social Sciences (SPSS) computer programme version 20.0. The findings showed there is a relationship between teachers’ attitude towards teaching of HIV/AIDS education and students’ knowledge and attitudes towards sexual behaviour. The study recommends that teachers should change their attitude towards teaching HIV/AIDS education.