We have synthesized and structurally characterized novel peroxovanadium(V) compounds containing amino acid derivatives as ancillary ligands; N-(4-imidazolylmethyl)-L-alanate (imala) and N-(4-imidazolylmethyl)-L-phenylalanate (imphe). The structure of the imala complex was determined using X-ray crystallography. These compounds stimulated the proliferation of H4IIEC3 rat hepatoma cells at low doses but were cytotoxic at high doses. They also exhibited insulin-mimetic effects.