The title compound, C7H7NO2, was synthesized via a one-pot Vilsmeier–Haack and subsequent Friedel–Crafts reaction. The pyrazole ring makes dihedral angles of 4.50 (9) and 2.06 (8)°, respectively, with the aldehyde and acetyl groups. In the crystal, classical N—H⋯O hydrogen bonds and weak C—H⋯O inter­actions assemble the mol­ecules into a chain along the b axis.

In the title compound, C16H14N2O, the benzimidazole ring system is essentially planar. The planes of the benzene rings make a dihedral angle of 85.92 (8)°. In the crystal, neighbouring molecule are connected into paris along the c axis by weak C—H⋯O interactions and the connected pairs are expanded through C—H⋯N hydrogen bonds and C—H⋯π interactions along the b axis.