This paper presents experimental investigation on thermal properties (thermal diffusivity and thermal conductivity) of AM series cast magnesium alloys. The effects of the changing in Al content (from 2 to 9 Al and constantly 0.5 Mn, wt. %) in the alloys on thermal properties, density and hardness were comparatively analyzed. It was observed that intermetallic phases (Mg17Al12 ve Al8Mn5) found in the microstructure of the alloys have an effect on thermal diffusivity, thermal conductivity, density and also hardness. The thermal properties of the alloys were decrease with increasing Al content in the alloy. The thermal properties of the alloys were increase with increasing temperature (the temperature range from 25°C to 400°C). The highest thermal diffusivity was measured on AM20 alloy and the lowest thermal diffusivity were observed on AM90 alloy.