Some phthalimidyl azo dyes containing N,N-diethyl or N,N-di($eta$-methoxycarbonylethyl) group have been attempted to apply onto two kinds of polyurethane based materials and rationalize their dyeability and fastness comparing with those of some commercial disperse dyes. Phthalimidyl azo dye showed 66~98% of exhaustion yield at $120^{circ}C$ by a conventional exhaust dyeing method. The dyeings were found to have a higher wash fastness with both fabrics in comparison with those of commercial dyes which indicates lower thermomigration and efficient alkali clearable properties of phthalimidyl ring and/or diester group during post-dyeing process.