The central problem of this study was to trace the influence of socio-economic factors on transition  from primary to secondary school level in  Mwingi central Sub County; Kitui County. The transition rate to secondary school in Mwingi Central District stood at 66.5% in 2015, a transition rate below the government target of 70%. The study sought to establish the factors that influence transition to secondary school. The study also sought to relate the parental level of education and transition of pupils from primary to secondary school. The influence of household income on transition to secondary school and sibling position were also examined. The study employed descriptive survey design and correlation research design to establish the socio-economic factors influencing transition from primary to secondary education in Mwingi Central District.is study was based on “ Classical Liberal theory of Equal Opportunity and Social Darwinism” advanced by Charles Darwin (1982). Simple random sampling was used to select samples of fifteen (15) secondary schools from a population of thirty nine (39) secondary schools.  The target population of the study consisted of all the 4820secondary school students (form one to form three) in Mwingi central district, four area chiefs. Three hundred and fifty seven secondary school students were used as the representative sample. A sample of fifteen K.C.P.E graduates who had not transited to secondary school was also interviewed. The study utilized a questionnaire as a research instrument to collect data. An interview schedules for Area chiefs and fifteen (15) class eight graduates who did not transit to secondary school in the past three years was used to collect data that may not be directly observed. Responses from questionnaires and interview guides were organized according to pertinent aspects of the study. Descriptive statistics including percentages, mean, frequency counts were used to analyze the data obtained. The results of the data analysis were presented in frequency tables, pie charts and bar graphs. The study found that level of parents’ education influence transition to school most, followed by level of income and gender socialization factors. The study also found a linkage between sibling position and transition to secondary education. The study recommends sensitization of the community on the need for education of boys as well as that of girls. The study also recommends that the government should subsidize secondary education on the basis of financial background of the learner. The study also recommends that adult education should be availed to those who have not had access to formal schooling in the past especially the parents. Finally the study recommends that clear penalties to parents who withhold their children from secondary school be defined.