There is provided a positive resist composition excellent in transparency, heat resistance, and refractive index particularly for forming a microlens and for forming a planarization film; and a microlens and a planarization film formed from the positive resist composition. A positive resist composition comprising a component (A): an alkali-soluble polymer comprising a unit structure having a biphenyl structure; a component (B): a compound having an organic group to be photolyzed to generate an alkali-soluble group; and a component (C): a solvent. The positive resist composition wherein the alkali-soluble polymer as the component (A) is a polymer comprising a unit structure of Formula (1): where when the total number of unit structures constituting the polymer (A) is assumed to be 1.0, the ratio n1 of the unit structure of Formula (1) constituting the polymer (A) satisfies 0.3≦n1≦1.0.