To obtain a monoazo compound which dyes a hydrophobic fiber material in clear blue having excellent fastness by diazotizing a specified 4- nitrocyanine and coupling the product with a 3-N-substituted aminoalkylsulfonylaminobenzene.

A product obtained by diazotizing a 4-nitrocyanine represented by formula I (R1 is cyano or nitro; and R2 is cyano, Cl or Br) is coupled with a 3-N-substituted amino-alkyl (or -phenyl)sulfonylaminobenzene represented by formula II [R3 is a phenyl or an (un)substituted linear or branched alkyl; R4 is H, Cl, Br, an (un)substituted linear or branched alkyl; R5 is an (un) substituted linear or branched alkyl, an (un)substituted linear or branched alkoxy or the like; R6 is Cl, Br, cyano or the like; X is O or methylene; and n is such an integer that the total number of carbon atoms of a divalent group: -(CH2)n-X- is 1-6] to obtain a monoazo compound represented by formula III.