NEW MATERIAL:A thiazole derivative expressed by formula I (R1 is H, hydroxyalkyl, hydroxyiminoalkyl, alkoxyiminoalkyl, formyl, carboxy, cyano, nitro, halogen, thiocayanate or formula III; R2 is H, alkyl, alkanoyl or alkoxycarbonyl; A1 is alkylene; R3 and R4 are H or alkyl or R3 and R4 together form pyrrolidine ring, piperidine ring, morpholine ring or piperazine ring, provided that R2 is alkanoyl or alkoxycarbonyl when R1 is H) or a salt thereof.

EXAMPLE: 4-(3,5-Di-tert-butyl-4-hydroxyphenyl)-5-formyl-2(3H)-thiazolone.

USE: An anti-inflammatory agent, antipyretic agent, analgesic agent, antiarthritic agent, antirheumatic agent and immunological function regulator.

PREPARATION: For example, a compound expressed by formula II is subjected to the Vilsmeier reaction to afford the aimed formyl compound expressed by formula Ia.