The study investigated role differentiation and job performance of administrative staff in tertiary institutions in Rivers State. The research design for the study was correlational. A sample size of 250 was drawn from a population of 400 consisting of administrative staff in the offices of (HODs, Deans, Bursar, directors and other principal officer) and principal officers in tertiary institutions in Rivers State. The study used two sets of questionnaires directed at the two sets of respondents. Stratified sampling technique was adopted. The tertiary institutions included the Rivers State University, Ignatius Ajuru University of Education, Port Harcourt, Capt. Elechi Amadi Polytechnic, Port Harcourt, Ken Saro Wiwa Polytechnic, Bori and Rivers State College of Health Management Technology. Out of the 250 questionnaire instruments distributed, 235 or 94% were duly completed and returned. The analysis of this study was based on the returned copies. Two research questions and two null hypotheses were posed. The descriptive statistical of tool of mean and standard deviation was used in answering the research questions while Pearson Product Correlation Coefficient (PPMC) was used in testing the research hypotheses. The questionnaires were validated by the researcher’s supervisor in the department of Educational Management Ignatius Ajuru University of Education, Port Harcourt. The reliability of the instrument was tested using the Crumbach Alpha (SPSS version 23) and obtained .971>.71 which showed that the instrument was highly reliable. The findings showed that principle of unitary command, job rotation, and delegated duty are significantly related to greater performance of admin staff in tertiary institutions in Rivers State. The study recommended among others that administrators should endeavour to allocate roles to staff according to the staff competences, attitude, skills and job description.