PURPOSE: To provide a water-soluble triphenedioxazine compd. which is usable as blue fiber-reactive dyestuff for cellulose fibers, particularly cotton, wool, and nylon by preparing a compound having a structure represented by a specified formula.

CONSTITUTION: This compsn. is represented by formula I {wherein M represents H or an alkali metal; m is 1 or 2; X presents H, a halogen, a (substd.) 1-4C alkyl, a (substd.) aryl or the like; R1 and R2 each represent H, a (substd.) 1-6C alkyl, or a (substd.) aryl; Z represents a residue represented by formula II (wherein Y1 and Y2 represent each a vinyl group or alternatively ethyl or β-hydroxyethyl substd. in the β-position by a substituent which can be eliminated with an alkali to form a vinyl group, provided that Y1 and Y2 do not simultaneously represent β-hydroxyethyl; and W1 and W2 each represent a 2-6C alkylene); A represents a covalent bond, a group represented by formula III [wherein R3 has the same meaning as R1; B1 represents a 2-6C alkylene, a 3-10C alkylene (interrupted and substd. by a hetero group)] or the like; Z0 represents H or a group represented by formula IV (wherein Y3 and Y4 have each the same meaning as Y1; W3 and W4 have each the same meaning as W1; and A0 a covalent bond or a group represented by formula V (wherein R4 has the same meaning as R1; and B2 has the same meaning as B1) or the like}.