BACKGROUND: Long-chain cellulose esters can be used as packaging materials, film materials, biodegradable plastics and drug delivery agents. Chemical methods are commonly adopted for preparation of these esters using traditional chemical catalysts and organic solvents, which result in environmental and safety problems. RESULT: A new enzymatic method was tested for synthesis of long-chain cellulose esters in mixed ionic liquids. The key reaction conditions, including mass ratio of ionic liquids, acylating agents, lipase/cellulose mass ratio, reaction temperature and substrate molar ratio, showed significant influences on enzymatic acylation. FT-IR and H-1 NMR spectra indicated the successful acylation of hydroxyl groups. SEM and XRD data showed significant changes in morphologies and crystallinity. The thermal properties of products were different from the original due to the disruption effect of ILs and the enzymatic acylation. CONCLUSION: A facile one-step route is presented for synthesis of long-chain cellulose esters. The lipase-catalyzed synthesis is an ecofriendly and green approach for the modification of cellulose by replacing traditional chemical catalysts with enzymes and replacing organic solvents with ionic liquids. This biocatalytic approach may find its applications in preparation of potentially biodegradable materials for food, pharmaceutical and related industries. (C) 2016 Society of Chemical Industry