The work herein was focused to study the effect of the microplastics on the yield and quality of biocrude (BC) produced by hydrothermal liquefaction (HTL) of real municipal sludge (RMS). HTL experiments with RMS containing 3 % w/w microplastics were conducted at 325 °C and 30 min both in the absence and in the presence of CoMo/Al2O3, NiMo/Al2O3 and activated carbon felt (ACF) as heterogeneous catalysts. A white wax was isolated from BC with a yield of 5, 8 and 6 % w/w daf when CoMo/Al2O3, NiMo/Al2O3 and ACF were used respectively. GC-MS analyses demonstrated that oleamide was present in the wax while FT-IR analyses showed the presence of chlorinated organic compounds, affecting negatively the BC quality. HTL experiments with mixture of microalgae and controlled amounts of polyvinylchloride, polyethylene and nylon 6,6 at 325 °C for 30 min confirmed that wax is originated from hydrothermal conversion of synthetic polymers.