This work includes optimization of the AZ91 magnesium alloy cold chamber die casting process by experiments conducted according to the Taguchi experimental technique, to find the effective process parameters which determine the mechanical and metallurgical properties of the casting products. Optimum process parameters determined according to the test results are 660 degrees C for bath temperature; 200/250 degrees C for die temperature; 0.30 vol.% for protective gas concentration; 120 MPa for intensification pressure and 30 ms(-1) for gate velocity. These parameters result in minimum porosity formation which provides high mechanical strength and density and good metallurgical properties. AZ91 alloy samples manufactured with the optimum process parameters show dimensional tolerances of +/- 0.04 mm, density of 1.78 gcm(-3), less than 2% porosity in average, maximum yield strength of 157 MPa and ultimate tensile strength of 248 MPa and maximum elongation of 7.67% in a 50 mm sample. Finally, surface modification of Mg die casting parts is crucial for meeting the long term usage requirements of the consumers. The electroless/electro nickel-plating with appropriate baths and pre-treatment processes were applied for providing fine surface conditions. The most effective process and modification parameters were analyzed in this study by considering the product quality.