In this work, long glass fibre reinforced polypropylene/intumescent flame retardants (LGFPP/IFR) composites are exposed to ultraviolet (UV) radiation with wavelength of 340 nm for 0-800 h. The effects of UV ageing on the flame retardancy, thermal stability and mechanical properties of LGFPP/IFR composites are investigated and discussed by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), mechanical properties and energy dispersive X-ray analysis (EDAX). A slight variation in LOI values and UL-94 levels are observed, and CCT results display a lower heat release rate for all aged samples. The TGA result also shows that aged samples have a higher degradation temperature with the prolongation of the aging time. EDAX showed higher content of the O, P and N elements on the surface of samples after 600 h ageing, which means partly gathering of IFR particles. The tensile, bending and impact strengths decrease after ageing, and the fracture morphology shows that interface debonding occurs.