Biodiesel in the past, was once considered a fringe fuel. However today, the production and consumption of this fuel has grown as a sustainable and much more eco-friendly alternative to the Conventional diesel (Petroleum diesel), for diesel engines; if not in pure form, it will be in blends of different ratios, or as a fuel additive, to improve engine performance and ensure longevity. In this research, oil from Mango (Mangifera indica) seed was extracted through Soxhlet solvent process, and converted into biodiesel by the method of Transesterification. This process involved the reaction between the extracted oil and methanol at an optimal temperature of 60°C, and 1%w/v of the catalyst (KOH) concentration for optimal yield of biodiesel. The produced biodiesel was analyzed and evaluated by comparing its physical characteristics to that of Conventional (petroleum) diesel fuel. The properties analyzed were; Density, Heating value, flash point, specific gravity, viscosity, cloud point, water content and pour point. The biodiesel from mango seed oil (MSO) compared excellently well with the values obtained for the commercially available petroleum diesel, dispensed at government approved filling stations in Nigeria. The biodiesel so produced and characterized, was subsequently subjected to an engine test, in a four-stroke internal compression (IC), (diesel) engine loaded between 120 – 200 rpm, to determine its suitability as a fuel. The result was compared with the Conventional diesel characteristics in terms of brake power output, mass flow rate, thermal efficiency, and specific fuel consumption (SFC) and so on. The biodiesel results compared very well with most of the data generated on the conventional diesel, and satisfied the ASTM-D6751 and the EN14214 standard requirements for suitability as working fluid in an IC engine, especially with regard to SFC, which translates to the direct running cost of every diesel engine.