Diffusion bonding of gray cast iron to gray cast iron experiments were carried out in air atmosphere and in inert gas (Argon) under different pressing load, temperatures and time to find the optimum bonding condition experimentally which affect the bond strength. The pressing load are 1 and 2 ton, the bonding temperatures are 700, 750, 800, 850, and 900ºC, and bonding time 15, 30 and 60 min. To evaluate the bond strength the shear test investigation was performed, the actual bonded area was calculated by using a computer package called (Auto Cad 2006). After calculating the bonded area, shear strength values were predicted for each bonded specimens, the results show that the bond strength increases with increasing the temperature, the bonding temperature brings about an improvement in bond strength but to a certain limit only. Any further rise in temperature will impair the strength owing to a grain growth as well as increasing carbide precipitation. Bond strength also increases with bonding time, the increase in bonding time has a positive effect up to a certain limit, any excessive holding time impairs bond strength. The highest value of shear strength of gray cast iron to gray cast iron joints is (155.7 MPa) at bonding temperature of 900ºC for 30 min holding time under pressing load of 1 ton. Improvement in the bond strength when the pressing load raises mainly attributable to the increase in the area of actual contact between the mating surfaces. Pressing load will raise bond strength up to a certain value, any further increase in pressing load reduces it. It found that the bond strength increases with increasing pressing load . For inert gas (Argon) experiments. No reliable results are obtained for the bonded during shear test may be due to abominable argon gas and this prevents forming of bond. Vickers microhardness testing was carried out to measure hardness distribution in gray cast iron joint. Vickers microhardness testing was performed on unetched specimens using 0.9 Kg load with 15 sec indentation time. The results observed from microhardness test show that the hardness increases with increasing bonding temperature due to formation of hard phased iron carbides (Fe3C). Microstructure of the interface was carried out by using optical microscope before and after the experiment. The microstructure results show the formation of carbide and the carbide precipitation increases with increasing the bonding temperature and time.