Four novel 5-acyloxyimino-5-deoxyavermectin B1 compounds have been synthesized from avermectin B1 by selective oxidization of the hydroxy group at C-5, followed by oximation and convenient esterification. Their structures were confirmed by IR, H-1 NMR, C-13 NMR and MS. Insecticidal activities of the intermediate oxime and the four new acyl derivatives were evaluated against Helicoverpa armigera, Spodoptera exigua and Musca domestica. (C) 2004 Society of Chemical Industry.