The present invention provides a positive-working photosensitive composition which comprises (a) a basic nitrogen-containing compound having a polycyclic structure represented by formula (I) and (b) at least one of compounds represented by formulae (II) to (IV) defined in the specification: wherein Y and Z may be the same or different and each represent a straight-chain, branched or cyclic alkylene group, which may contain a hetero atom or may be substituted. The positive-working photosensitive composition which exhibits no reduction of width of resist pattern or no T-top deformation of surface shape of resist pattern with time between after exposure and heat treatment without causing sensitivity drop.