The depletion of fossil fuels and the worst impact on environmental pollution caused of their burning have led to the search for renewable clean energies. Bio-diesel is an alternative to petroleum-based fuels derived from a variety of feed-stocks, including edible and non-edible oils, animal fats, and waste cooking oil. At present, bio-diesel is mainly produced from conventionally grown vegetable oils such as cotton-seed, mahua, sunflower, rapeseed, jatropha, palm and soybean. The cost of bio-diesel is the main obstacle to commercialization of the product. Bio-diesel produced from edible oils is currently not economically feasible. On the other hand, extensive use of edible oils for bio-diesel production may lead to food crisis. Bio-diesel is just one source, but a very important one. The contribution of cotton-seed as a source for bio-diesel production will be of great importance in the coming day. In India cotton-seed plant is a widely grown up termed as a divine tree due to its wide relevance in many areas of study. The present work deals with bio-diesel production from raw cotton-seed oil, which is mono-ester produced using transesterification process. It has high lubricity, clean burning fuel and can be a fuel component for use in existing unmodified diesel engine. Filtered cotton-seed oil (bio-diesel) can be used as a substitute fuel for diesel engines because the properties like calorific value, specific gravity, and viscosity are very much comparable with conventional or normal diesel fuel.