Thermal conductivity is an important property when high heat dissipation is a requirement during the use of the cast component. This study was carried out to study the effect of heat treatment on thermal conductivity of three common aluminum die casting alloys. Measurement of thermal conductivity was done by the Hot Disk method. A substantial increase in thermal conductivity was measured as a result of heat treatment. Microstructural changes due to heat treatment was examined by optical and scanning electron microscopy.