Multi-material structures combining magnesium alloys and engineering plastics have attracted increasing attention as an effective approach to weight reduction in the transportation industry. A promising joining method with high productivity is injection molding joining, whereby a metal insert is placed in a mold and is then integrated with molten resin. Along with appropriate surface treatments, such joining is fundamentally important to achieve high joint strength. Moreover, because magnesium alloys have poor corrosion resistance, surface treatments that improve corrosion resistance are necessary. This study investigated the effects of laser irradiation and subsequent anodizing and conversion treatments on the joining properties of AZ91D magnesium alloy and polyphenylene sulfide（PPS）resin after injection molding joining. Laser irradiation formed surface asperities on the AZ91D alloy, leading to strong mechanical interlocking and joint strength sufficiently high to fracture the PPS resin. However, when surface asperities are excessively deep, incomplete resin filling at the bottom of the asperities occurred, leading to reduction in joint strength. For conversion-treated specimens, joint strength increased concomitantly with decreasing laser scanning speed, but anodized specimens showed only limited improvement because fracture occurred within the anodic oxide film. These findings from injection molding joining experiments demonstrate that both resin filling into surface asperities and the mechanical properties of surface films are crucially important factors governing joint strength.