This paper focuses on the determination of the interfacial heat transfer coefficient (IHTC) at the metal-die interface in the high pressure die casting (HPDC) process. Experiment was conducted and a "step shape" casting was used to cast a magnesium alloy AM50 against a HI 3 steel die. Based on the temperature measurements inside the die, IHTC was determined by applying an inverse approach. The influences of the step thickness and process parameters on the IHTC were investigated. Results show that the shape of IHTC profiles is different at different steps and the duration for IHTC to maintain a higher value grows as the step thickness increases. The influence of process parameters is mainly on the IHTC peak value. For thinner steps, a higher fast shot velocity leads to a higher IHTC peak value. But for thicker steps such as Step 5, the casting pressure shows a more prominent influence on the IHTC peak value. Also, at these thicker steps a lower initial die surface temperature always leads to a higher IHTC peak value. (C) 2008 Elsevier Ltd. All rights reserved.