In order to fully achieve the benefits of rubber toughened polymers, a deep understanding of the fracture behavior; particularly under mixed-mode loading conditions is needed. In this investigation, the mixed-mode fracture of poly(methyl methacrylate)/graft-acrylonitrile butadiene styrene (PMMA/g-ABS) blends with different weight percentages of rubber (0, 10, 15, and 20) was studied by essential work of fracture (EWF) method. The effects of ligament length, rubber content, and different mixed-mode loading angles on the fracture toughness were studied and macroscopic and microscopic deformations taking place at the front of crack tip and in the bulk of the specimen were investigated. The results indicated that, with the increasing rubber contents and decreasing loading angles the total specific work increases significantly. The maximum value of essential and the non-essential work of fracture in pure mode-II and in pure mode-I belonged to 20% rubber content and the minimum value of essential and the non-essential work of fracture in pure mode-II and in pure mode-I belonged to pure PMMA. The highest value of the ultimate elongation length belonged to pure mode-II of loading angle in all of the compositions. The total specific work of pure PMMA was not considerable in comparison to other rubber contents.