To provide a method for producing an acid modified polypropylene resin which has a large graft amount of an acid and, simultaneously, excels in productivity, and to obtain an acid modified polypropylene resin produced by the production method.

The method for producing the acid modified polypropylene resin comprises compounding (A) 100 pts.wt. polypropylene resin, (B) 0.1-20 pts.wt. unsaturated carboxylic acid and/or its derivative, (C) 0.1-20 pts.wt. organic peroxide having a decomposition temperature at which the half-life period comes to one minute being 50 to 120°C, (D) 0.01-20 pts.wt. organic peroxide having a decomposition temperature at which the half-time period comes to one minute being 150 to 200°C, and melt kneading the resulting compound.