In the title mol-ecule, C(12)H(12)N(2)O, the five- and six-membered rings form a dihedral angle of 68.41 (16)°. The aldehyde group is nearly coplanar with the pyrazole ring [C-C-C-O torsion angle = -0.4 (5)°]. The three-dimensional architecture is sustained by weak C-H⋯O and C-H⋯π inter-actions.