AC2A is a gravity cast aluminium alloy which has been widely used particularly in the automotive industry due to its good castability, weldability and pressure tightness. Even though aluminium gravity cast parts has less porosity trouble than those produced using other die casting processes, little porosity is still not allowed for automotive parts with safety requirement such as brake cylinder, fuel rail, oil pump housing, power steering valve box and clutch cylinder. This work aimed to investigate effects of cooling rate and melt treatment on porosity level of gravity casting AC2A aluminium alloy. Aluminium was performed by gravity casting method. Different mold material and degassing agent addition were used to obtain different controlled level of cooling rate and melt quality, respectively. The different mold was effected to cooling rate and porosity. Lowest porosity level was found in castings produced using graphite mold with degassed melt while slightly higher porosity level was presented in castings produced using steel mold with similar melt treatment. Level of porosity presented in the castings was discussed in terms of dendritic grain size and melt quality. Gravity cast with a high cooling rate using appropriate degassed melt was recommended for sound castings.