A positive photosensitive composition comprising (a)a resin soluble in an aqueous alkali solution containing a specific structure unit; (b) a compound which generates an acid with irradiation of an active ray or radiation; and (c) a low molecular weight acid-decomposable dissolution inhibitor having a molecular weight of not more than 3000, which possesses a tertiary alkyl ester group and whose solubility in an aqueous alkali solution is increased by the action of an acid; wherein compound (c) is a compound having at least two tertiary alkyl ester groups, in which the longest distance with respect to the distance between two tertiary ester groups selected arbitrarily comprises at least 10 bonding atoms except for the atoms contained in the ester groups or a compound having at least three tertiary alkyl ester groups, in which the longest distance with respect to the distance between two tertiary ester groups selected arbitrarily comprises at least 9 bonding atoms except for the atoms contained in the ester groups. The positive photosensitive composition has a high sensitivity, high resolution and good profile and excels in storage stability and heat resistance of the resist solution.