Coating of materials is one of the known surface modification technique in recent years and electroless method is one of the growing areas of both scientific and commercial region. An optimal formulation for electroless Ni-B coating is developed. After doing successful Ni-B coating, nano-sized diamond particles are incorporated into the coating to improve hardness and wear resistance properties of the deposits. To disperse diamonds to the bath, five different suspensions are prepared and also five different electroless composite Ni-B coatings are obtained. The rates and microhardness of coatings after in as-plated and heat-treated conditions are measured. The better composite coatings are chosen to study. SEM examination and then wear test (ball on plate) is done to the nano-composite coatings, electroless Ni-B coating and uncoated plain carbon steel substrates. Microhardness of the nano-composite coatings greatly increased because of the presence of the nano particles. The hardest electroless composite coating (1250 HV(100)) is 30 times more resistant to wear than steel material, 14 times more resistant than electroless Ni-B coatings.