The study sought to investigate the extent and effect of implementation of gender mainstreaming policy in public secondary schools in Msambweni Sub – County in Kwale County, Kenya. Anecdotal reports alleged that in most public institutions in the country, gender stereotyping was still rife and persons of one gender still predominantly held the lion‘s share of available opportunities. This implied either non-implementation of gender mainstreaming policy by the institutions‘ management or their reluctance to subscribe to the requirements of the tenets of the policy. Specifically it meant that the process of implementation of gender mainstreaming policy could be facing some obstacles thus the reluctance by the institutions to embrace its practice. The problem was compounded by the fact that there was minimal empirical data on the extent and effects of the process of implementation of gender mainstreaming policy particularly in marginal areas such as Msambweni Sub – County. A descriptive survey study was therefore proposed to provide data to help seal the existing research gap. The study sought to; find out the attitude of schools‘ principal towards gender mainstreaming policy, determine the composition of students council by gender, establish the composition of school workers by gender, determine the distribution of positions of subject heads and heads of departments by gender, determine the gender composition of school principals and deputy principals and identify the challenges of the process of implementation of gender mainstreaming policy in the Sub – County. A sample of 20 Principals from 20 public secondary schools participatedin the study. Data was collected using questionnaires  consisting of open and closed ended items.