An object of the present invention is to provide an acrylic pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive, which has excellent adhesiveness to an adherend having surface polarity of every kind and can exhibit excellent repulsion resistance even in a moist heat environment, and a pressure-sensitive adhesive sheet using the composition. The pressure-sensitive adhesive composition provided by the present invention contains a copolymerization reaction product of a monomer mixture. The monomer mixture contains an alkyl (meth)acrylate having an alkyl group with a carbon number of from 4 to 20 and N-vinylcaprolactam. The total sum amount thereof is 95% by mass or more of the whole of monomer components. An amount of N-vinylcaprolactam is from 12 to 40% by mass.