In the present research, the diffusion of prepared sample blends (PP/PC) unfilled-filled with different amounts of carbon black (2 – 7) wt% and at different temperatures (25oC, 40oC and 55cC) were studied. Absorption test was carried out in (Gas-Oil and Diesel-Fuel) at different immersion times as: Two equations were used to calculate the diffusion coefficient values. In the first equation , the diffusion coefficient values ranged from (0.252 to1.619) cm2/sec for immersed in Gas-Oil and it ranged from (0.321 to 1.783) cm2/sec for immersed in Diesel-Fuel. In the second equation the diffusion coefficient values ranged (0.37 to 2.649) cm2/sec for immersed in Gas-Oil and it ranged from (0.562 to 2.635) cm2/sec for immersed in Diesel-Fuel. It was found that the results obtained by the two equations were approximately the same. Indeed the blend (PP/PC) filled with (4 wt%) of carbon black has the lowest values of diffusion coefficient (calculated by the above two equations) in Gas-Oil and Diesel-Fuel which indicates this sample has better performance than other samples. The diffusion test also was carried out at different temperatures in order to show the effect of temperature on diffusion coefficient. It was found that the diffusion coefficient values increase with increasing temperature. All these samples are obeyed Fickian behavior and the activation energy (E) increases with increasing amounts of carbon black (2 – 7) wt%.