The present invention provides antifouling coating compositions having excellent long-term storage stability and provides an antifouling coating composition that can maintain the stable dissolution and antifouling performance of a coating film without causing coating film defects such as cracks in seawater for a long term, such that an antifouling coating film having increased environmental safety can be formed. The present invention provides an antifouling coating composition containing: (A) a triorganosilyl ester-containing copolymer obtained from a mixture of (a) a triorganosilyl (meth)acrylate monomer represented by general formula (1): (here, R1 is a hydrogen atom or a methyl group; and R2, R3, and R4 are the same or different from each other and each represents a C3-6 alkyl group branched at the α-position or a phenyl group) and (b) an ethylenically unsaturated monomer copolymerizable with the triorganosilyl (meth)acrylate monomer; and (B) calcium sulfate hydrate.