To provide an acid-modified polypropylene resin which can be used for an adhesive capable of bonding a polyolefin type resin and a polar resin with sufficient force, its production process and a resin composition using it.An acid-modified polypropylene resin, which is obtained by grafting an organic acid component to a polypropylene resin, wherein the polypropylene resin is an isotactic polypropylene resin, the grafted amount X (wt %) of the organic acid component in the acid-modified polypropylene resin is within a range of from 1.0 wt % to 20.0 wt %, and the melt flow rate Y (g/10 min) of the acid-modified polypropylene resin satisfies the expression: Y≦18.5 exp(0.82X), a process for producing such an acid-modified polypropylene resin, a resin composition using it and a laminate.