A change in dimension of a pattern formed of a polysilsesquiazane photosensitive composition containing a photoacid generating agent is prevented. The photosensitive composition according to the present invention is characterized by comprising: a modified polysilsesquiazane having a weight average molecular weight of 500 to 200,000 comprising basic constitutional units represented by formula --[SiR.sup.1(NR.sup.2).sub.1.5]-- wherein R.sup.1's each independently represent an alkyl group having 1 to 3 carbon atoms or a substituted or unsubstituted phenyl group; R.sup.2's each independently represent hydrogen, an alkyl group having 1 to 3 carbon atoms, or a substituted or unsubstituted phenyl group, up to 50% by mole of said basic constitutional units having been replaced by a linking group other than the silazane bond; a photoacid generating agent; and a basic material.