There is disclosed a resist composition that remarkably improves the resolution of photolithography using a high energy beam such as ArF excimer laser light as a light source, and exhibits excellent resistance to surface roughness and side lobe under use of a halftone phase shift mask; and a patterning process using the resist composition. The positive resist composition at least comprises (A) a resin component comprising a repeating unit represented by the following general formula (1); (B) a photoacid generator generating sulfonic acid represented by the following general formula (2) upon exposure to a high energy beam; and (C) an onium salt where a cation is sulfonium represented by the following general formula (3), or ammonium represented by the following general formula (4); and an anion is represented by any one of the following general formulae (5) to (7).