The title compound, C(20)H(19)N(3)O, exists in a keto-enamine tautomeric form. The pyrazolone ring makes dihedral angles of 20.52 (10) and 77.73 (5)° with the two phenyl rings and an intra-molecular N-H⋯O hydrogen bond occurs. A weak inter-molecular C-H⋯O hydrogen bond is observed in the crystal structure. The allyl group is disordered over two positions, with site-occupancy factors of 0.533 (5) and 0.467 (5).