Growing interest in utilizing and processing natural fibres (NF) to create biodegradable and sustainable composites as environmental concerns upsurge globally. Date palm trees (DPT) account for more than 4.5 million tons of waste annually worldwide, making it one of the most abundant agricultural biomass waste in the MENA region. This study evaluated the biological resistance of thermoplastic composites developed from polylactic acid (PLA) and recycled polyvinyl chloride (RPVC) reinforced with date palm fibre (DPF) at different contents (10, 20, 30, 40 wt.%) and fibre size (250 – 500 µm and ≥1,000 µm). Composites where exposed to the brown-rot fungus; Irpex lacteus, and white-rot fungus; Tyromyces palustris, to evaluate its resistance to biodegradation. Results showed that composites developed using PLA had higher weight loss (%) when compared to the same samples but reinforced with RPVC. Composites with higher DPF content showed high rates of decay when used with different polymer matrix. Also, DPF length had a significant effect on the disintegration of the composites. DPF/PLA reinforced with 40 wt.% DPF showed the highest weight loss (WL%) reaching 5.61% and 5.46% when exposed to Tyromyces palustris and Irpex lacteus respectively. On the other hand, the biodegradation had a direct impact on the disintegration of the composites developed where the WL%, of PLA composites developed with 40 wt.% DPF showed 61.40%.