This study investigated the effect of relationship marketing strategies on customer retention in Postal Corporation of Kenya, Nairobi region. The following theories guided the study; commitment-trust theory, transactional cost theory, customer engagement marketing theory and customer service theory. Descriptive research design was used in the study. The study targeted three hundred managers from sales and marketing department, customer care department and operations department. The study used one tenth of the target population for pilot study that is thirty respondents. Content validity of the instrument of study was tested through expert opinion. Cronbach's alpha reliability experiment was used to evaluate the consistency of the questionnaires, which met a reliability threshold of alpha ≥ 0.70. The study sample size was thirty percent of the total population that is ninety managers. The sampling technique used to identify respondents was simple random. Structured questionnaires were adopted to gather data, questionnaires were dropped and picked later. Data was examined using descriptive analysis and inferential statistics. Interpretation and presentation of information was through the use of tables accompanied by summaries of explanation. The study revealed that preferential treatment, customer rewards, relationship commitment and customer orientation had positively influenced customer retention in postal corporation of Kenya, Nairobi region. The study concluded that the corporation needs to embrace preferential treatment to esteem customers and develop more strategies of customer rewards to improve the level of customer retention. On relationship commitment and customer orientation, it concluded that the corporation needs to develop ways to enhance the commitment towards the delivery of the services while providing room for customers to be heard and served as a way of improving the relationship leading to improved customer retention. The study recommended that the top management should adopt relationship marketing strategies that aims at improving customer retention while promoting trainings to enhance implementation of the strategies. Survey needs to be done for informed reward strategy to customers and policies makers should bring policies that ensures customers are treated well.