PURPOSE: To prepare heat resistant polyamideimide resin soluble in a cresol type solvent by reacting a polyisocyanate compound, lactam and polycarboxylic acid having acid anhydride group at a specific ration in a cresol type solvent.

CONSTITUTION: A polyisocyanate (a) having a isocyanurate ring obtained by trimerizing a polyisocyanate compound (4,4'-diphenylmethane diisocyanate, tolylene diisocyanate or the like) under the presence of a catalyst at about 70W160°C, an aromatic diisocyanate (b), lactam (c) such as -caprolactam and a cresol type solvent (d) are reacted at about 160W190°C for 1W3hrs. thereafter polycarboxylic acid (e) having acid anhydride group such as trimellit acid anhydride is added and the reaction is continued at about 200W220°C for about 10W20hrs. moreover, to a total isocyanate equivalent, the component (a) is used at 3W30wt% and the component (c) is used at 30W80wt%.