Graft copolymer, method for preparing the same, and resin composition including the same

A method for preparing a graft copolymer, the method comprising:

• injecting and polymerizing a conjugated diene-based monomer and a mineral-based oil to prepare a rubbery polymer latex comprising a rubbery polymer (S10);
• injecting an alkyl (meth)acrylate-based monomer and an alkali metal sulfonate-based monomer in the presence of the rubbery polymer latex prepared in step (S10), and graft polymerizing to prepare a graft copolymer latex comprising a graft copolymer (S20);
• and
• injecting an aromatic vinyl-based monomer in the presence of the graft copolymer latex prepared in step (S20) and secondly graft polymerizing (S30),
• wherein the mineral-based oil comprises 70 wt % to 100 wt % of a mineral oil and 0 wt % to 30 wt % of a silicone-based oil,
• the mineral-based oil is injected in 0.2 parts by weight to 0.5 parts by weight based on 100 parts by weight of the conjugated diene-based monomer, and
• the alkali metal sulfonate-based monomer is injected in 0.8 wt % to 1.5 wt % based on the rubbery polymer and a total monomer amount injected.