Provided is a positive photoresist composition comprising (A) an alkali-soluble resin prepared by condensation of aldehydes and a mixture of phenols, which comprises (i) thymol, isothymol or a thymol-isothymol mixture and (ii) one or more of a phenol compound represented by the following formula (I); ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different, and each of them represents a hydrogen atom or a methyl group, and optionally, as a third monomer, (iii) a phenol compound other than m-cresol; (B) 1,2-naphthoquinonediazide-5-(and/or -4-)sulfonic acid esters as photosensitive agent; and (C) a low molecular weight compound having from 12 to 50 carbon atoms in all and from 2 to 8 phenolic hydroxy groups.