A thiophene-containing azo dye of the formula ##STR1## where R is substituted or unsubstituted alkyl, alkenyl, cycloalkyl or phenyl, X is hydrogen, halogen, hydroxyl, unsubstituted or substituted alkoxy, cycloalkoxy, phenoxy, mercapto, alkylthio, phenylthio, alkylsulfonyl, phenylsulfonyl or phenyl and Y is cyano, nitro, alkanoyl, substituted or unsubstituted benzoyl, alkylsulfonyl, phenylsulfonyl, Co-Z, where Z is unsubstituted or substituted phenoxy, amino, mono- or dialkyl-amino, pyrrolidino, piperidino, morpholino or N-alkyl-piperazino, and K is the radical of a coupling component is used as dyes for dyeing fiber material.