To obtain a new polyazo dyestuff having black color and blue to navy blue color, excellent in light fastness and moisture fastness, and useful for dyeing cotton, wool, leather, polyamide fibers, etc.

A compound of formula I [one of X1, X2 is hydroxyl group, and the other is amino; (p), (q) are each 0, 1; D1, D2 are each a group of formula II (R1 is H, a 1-4C alkyl, a halogen, etc.; R2 is H, hydroxysulfonyl, etc.); B is SO2-NH-A1-NH-SO2 (A1 is phenylene, etc.), etc.]. For example, a compound of formula III. The compound of formula I is obtained by combining a monoazo dyestuff of formula IV with a tetrazonium salt derived from a bisamino compound of formula V.