Tyrosinase (monophenol, O-diphenol: oxygen oxidoreductase, EC 1.14.18.1) is a copper-containing protein widely distributed in animals, plants and microorganisms. The enzyme was extracted from Cucurbitapepovar. cylindrica, (marrow, family:Cucurbitaceae). Proline, tryptophane, aspartic acid, cysteine, histidine, glycine, β-alanine and valinewere assayed for their effect on tyrosinase activity in different concentrations (2.5, 5, 7.5, 10 and 12.5 mM)in vitro. Histidine, aspartic acid, glycine and β-alanine induced tyrosinase activity gradually from 2.5 to 10 mM after which there was a decline in the enzyme activity. Tryptophane, valine and cysteine induced the activity up to 5 mM, while proline induced the activity from 2.5 to 7.5mM. Also, tyrosinase activity was assayed in presence of benzaldehyde, anisaldehyde (P-methoxybenzaldehyde) and acetaldehyde (0.1, 0.2, 0.3, 0.4 and 0.5 mM).It was found that the enzyme activity was inhibited by the three tested aldehydes.