To obtain a cationic 1,3,4-thiadiazole dye useful for inks, etc., for dyeing or textile printing of fibers, etc., or printing inks, by employing a specific molecular structure.

This dye is represented by formula 1 [R2 is 1-12C alkyl, 2-12C alkenyl or the like; R1, for example, is hydrogen, 1-12C alkyl, 2-12C alkenyl or the like when R0 is a group of formula II, and is 2-12C alkenyl, 4-8C hydroxyalkyl or the like when R0 is 1-12C alkyl substituted by cyano or hydroxyl; K is, e.g. a group in a coupling component of formula III (R3 is hydrogen, halogen, cyano, nitro, hydroxyl, 1-12C alkyl, 1-12C alkoxy or the like; R4 and R5 are each independently hydrogen, 1-12C alkyl, 2-12C alkenyl or the like; n is 1 or 2; and X- is anion)].