C9-C25 oxygen-containing compounds formed via the condensation reaction of furfuryl alcohol(FA) can be used as fuel intermediates for the production of bio-fuel. In this paper, the condensation reaction of FA was carried on over sulfuric acid catalyst in a batch aqueous phase reactor, in which the produced oligomers were separated from aqueous reaction system automatically before they went on further to form polymers. Reaction kinetics experiments showed that the values of reaction order of FA and sulfuric acid all were 1. The molecular structure and content of short chain-length oligomers B (C9-C25) were analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC) respectively. The molecular weight of FA condensate was determined by gel permeation chromatography (GPC). According to the information provided by GC/MS and GPC, we revealed that two polymerization mechanisms, step-growth polymerization and chain-growth polymerization, coexist in FA condensation reaction process in aqueous system. A simplified kinetics model based on the present mechanisms was established, and condensation products were divided into short chain-length oligomers B (C9-C25) and long chain-length oligomers C (>C25). •C9-C25 oligomers are produced in a batch aqueous phase reactor.•Oligomers can be hydrogenated to produce biodiesel.•Oligomers are separated automatically before they further form polymers.•Two polymerization mechanisms coexist in FA condensation reaction process.•A simplified kinetics model in quasi-homogeneous water system is developed.