This paper presents an experimental investigates of the bio-diesel preparation from vegetable oil ie mustard oil. The first time, the bio-diesel has been prepared by trans-esterification reaction or chemical process and blend in different proportion with diesel fuel. Again, without trans-esterification reaction, the mustard oil has been blended with diesel in a different proportion of 20%, 30%, 40%, and 50% and named as bio-diesel bland B20, B30, B40, and B50. The properties of the fuel ie density, viscosity, dynamic viscosity, carbon residue, flash point, fire point and calorific value of pure mustard and its blends have been carried out in the fuel testing laboratory. During the fuel and bio-fuel have been tested in the laboratory, different ASTM standards were maintained to find out the properties of the bio-diesel. The comparison was made between the blended bio-fuels which were prepared with or without trans-esterification reaction.