In recent years the number of applications of magnesium alloys in automobile power trains has increased due to alloy development and mainly due to increasing requirements for light weight constructions to save fuel and to reduce the emission of green house gases. For power train alloys the properties at elevated temperatures, especially creep properties are playing a major role. Magnesium alloys are here in competition with aluminium alloys and therefore an appropriate property profile is required in accordance with appropriate processing routes. High pressure die casting (HPDC) is the dominant casting process for manufacturing magnesium components. Several other processes have been developed in the last few years: Thixomolding® and New Rheocasting are semi-solid processes for the production of near net shape metal parts. Using the thixotropic properties of alloys, castings show a fine grained structure, less porosity compared to HPDC parts and improved mechanical properties. Moreover they offer the possibility to apply heat treatment for further improvement of properties. In this paper the creep properties of the new magnesium alloy MRI153 and of conventional AZ91-D are compared. Both alloys were cast by high pressure die casting, Thixomolding® and New Rheocasting. Creep tests on as-cast samples were performed at 150°C and for tensile stresses between 50 and 85 MPa. Besides density measurements, microstructural investigations were performed by using standard optical methods.