Fifteen novel aryl, substituted aryl and heteroaryl -hydroxy- (2a-e), -methoxyimino- (3a-e), and -benzyloxyimino- (4a-e) butyric acid methyl esters were investigated for their enzyme inhibition, and the synthesis of 10 compounds (3a-e, 4a-e) is given in this study. The other five compounds (2a-e) were synthesized before in another study. Compounds 3a-e and 4a-e were synthesized in this work as original compounds and characterized by H-1 and C-13 NMR, IR, mass, and elemental analyses. Their (E/Z)-isomerisation ratios were analyzed by H-1 and C-13 NMR. All of them are of pure (E)-configuration. Due to the literature survey, the elastase inhibition activity was not studied for these compounds. Elastase inhibition ability was investigated in this work for five -hydroxy- (2a-e), five -methoxy- (3a-e), and five -benzyloxyimino- (4a-e) butyric acid methyl esters. All these 15 compounds showed elastase inhibition activity. Compound 2b was the best one and exhibited a better activity than the standard ursolic acid whereas compound 2a worked like the standard. All these compounds can be novel elastase inhibitor agents in the pharmaceutical and cosmetic industries.