In spite of the development of various improved cultivars of maize, yield in Nigeria has continued to be hampered by the over cropped nature of most farmlands as well as a wide range of pests and diseases. This study therefore carried out an analysis of agro-chemical inputs’ use in maize production among small scale farmers in Iwo Local Government Area of Osun State. Specifically, the study investigated the relationship between agro-chemical inputs’ use and maize yield in the study area. It determined the factors affecting agro-chemical inputs’ use and the major constraints to its usage. Data was collected using a structured questionnaire from 105 respondents obtained through a two stage random sampling procedure. Analytical tools employed for the study included Pearson Moment correlation and linear regression analysis. The study revealed a 78.5% positive and significant relationship between agro-chemical inputs’ use and maize yield (p< 0.01). High cost and irregularity of supplies, insufficient farm income and fear of health hazards were the major constraints to the use of agro-chemicals. The determinants of agro-chemical inputs’ use among the farmers were; farm size, income at p<0.01 and educational status and household size at p<0.1. The study concluded that a strong positive relationship existed between agro-chemical inputs’ use and maize yield in the study area. It is recommended that there should be guaranteed minimum price for agricultural produce and that farmers should be empowered to increase their farm size through agricultural mechanization.