High density polyethylene (HDPE) was pyrolysed over different catalysts using an in-house designed laboratory fluidised-bed reactor operating in the 290-430 degrees C range under atmospheric pressure. The catalysts used were HZSM-5, Silicalite, HMOR, HUSY and SAHA and the yield of volatile hydrocarbons (based on the feed) was typically HZSM-5>HUSY approximate to HMOR>SAHA. Product streams varied markedly with catalysts type and structure. The sodium form of siliceous ZSM-5, silicalite, containing very few or no catalytically active sites, gave very low conversions of polymer to volatile hydrocarbons. HZSM-5 and SAHA produced more olefinic streams with HZSM-5 yielding over 80 wt% olefins in the C-3-C-5 range compared with around 40 wt% with SAHA. However, both HMOR and HUSY produced more paraffinic streams with large amounts of C-4 (19 and 14 wt%, respectively) and both catalysts deactivated during the course of the degradation. Observed differences in product yields and product distributions under identical reaction conditions can be attributed to the microstructure of catalysts.