The ambulance services industry in the country is very competitive, and most of the companies in the industry are facing service delivery challenges. This study analyzed the association between relationship marketing and sustainable competitive advantage in AMREF Flying Doctors, Nairobi. The specific objectives of the study included; determining the effect of use of technology on attaining sustainable competitive advantage, establishing the effect of customer retention on achieving sustainable competitive advantage, finding out the effect of customer satisfaction on achieving sustainable competitive advantage and determining the effect of customer trust level on attaining sustainable competitive advantage. The study used descriptive research design. The population of the study was made up of all the 167 headquarter-based-staff of AMREF Flying Doctors who are at the various supervision levels including, Head of departments, managers and team leaders. The study sampled 118 respondents, through a simple stratified random sampling method. Questionnaires were then administered to these respondents, in collecting data. Both reliability and validity were carried out on the data collection instruments. A pilot study was conducted at AAR Healthcare Head Office where an average Cronbach’s alpha reliability(α) value of 0.84 was recorded which implied acceptance of the instrument for use in data collection. Structured interview was used to collect additional data from customer relations manager. Data that is quantitative in nature was analyzed using SPSS while qualitative data was analyzed using summative content analysis and comparative methods. The results were then presented in figures and tables. The findings indicated that customer retention, customer satisfaction and customer trust have a strong positive relationship with sustainable competitive advantage; 0.733, 0.745 and 0.696 respectively. The association between use of technology and competitive advantage was a weak positive association (0.541). On the other hand, the regression analysis revealed that the independent variables; customer retention, customer satisfaction, use of technology and customer trust level explain up to 45.6% change in sustainable competitive advantage within the organisation. The study therefore recommends that in seeking to attain and sustain competitive advantage, AMREF Flying Doctors should keenly look at aspects associated with relationship marketing. Additionally, the organisation should seek to ensure complete, successful and intentional integration of most of its internal processes technologically in order to improve on service delivery and customer satisfaction hence customer retention. The study further recommends a research on relationship marketing and sustainable competitive advantage on the entire ambulance services industry so as to improve the applicability and reliability of the findings and recommendations in the industry. Other relationship marketing variables such as brand strategy and customer segmentation can also be evaluated against sustainable competitive advantage. The findings contribute to increased profitability in the industry as whole through enhanced performance. They also benefit the marketing professionals, managers and policy makers in understanding and implementing strategies and policies on relationship marketing and competitive advantage in the industry. The study also aids further research on other aspects of relationship marketing implementation and competitive advantage.