Accelerated weathering studies of untreated and treated oil palm fiber reinforced phenol formaldehyde composites and oil palm/glass hybrid fiber reinforced phenol formaldehyde composites were conducted. Thermal, water, biological and γ radiation effects on the composite properties were analysed. Mechanical properties such as tensile, flexural and impact properties of thermal and water aged samples were investigated. The extent of biodegradation and γ irradiation effects was estimated from variations in tensile and impact properties. The tensile and impact fracture mechanism and changes in fiber-matrix adhesion were studied using scanning electron microscopic analysis. The changes in the tensile and flexural stress-strain characteristics as well as deformation behaviour of aged composites are well explained by respective stress-strain curves. Mechanical performance of the composites decreased upon thermal ageing. Marked decrease in these properties of the composites is observed upon radiation ageing. However water immersion leads to an increase in strength properties in some treated composites such as on acetylation, silane, acrylonitrile grafting, isocyanate, permanganate treatment, alkali treatment etc. It is found that oil palm fiber increases the biodegradability of the composites.