This study assessed the effects of multiple components of municipal administrations on the functions of urban planning agencies in Nigeria, using Osun State as the case study. It examined the profile of the professionals across the levels of planning agencies in the state, the key activity areas of the planning agencies, operational parameters of the planning agencies, and the relationship between the planning agencies. Data used for the study were sourced from questionnaire administered on the heads of all the 35 planning agencies in the state. The study revealed that the agencies experienced conflict of interest in their operations and the reason for that was mostly jurisdictional. Also, the agencies seldom related with one another. The study concluded that the structure of municipal administration in Nigerian is responsible for proliferation of planning agencies and, consequently, the duplication of planning functions in the state, nay, Nigeria. It recommended, among others, legislative reform for effective municipal administration in the state and Nigeria, as a whole.