Coprocessing of Eucalyptus woodchips (EU) and low-density polyethylene (LDPE) has been investigated using two HBeta zeolites as catalyst. The reactions were carried out in a two-step (thermal/catalytic) system, varying the catalyst to feed (C/F) ratio. A maximum in the yield of the liquid organic fraction (oil*) was observed for both HBeta samples at intermediate C/F ratios due to the occurrence of sequential cracking reactions, which were accompanied by a significant reduction of the oil* oxygen content. This finding, together with the results obtained when feeding pure EU and LDPE, denotes that remarkable synergistic effects occur during the coprocesssing of lignocelllulosic biomass and polyolefinic plastics over HBeta zeolite, mainly by Diels-Alder condensation between furans and light olefins. The presence of acid sites with moderate strength in the HBeta samples is an essential factor to obtain high oil* yields since it limits the extension of severe cracking reactions.