Poly(p-phenylene benzobisoxazole) (PBO) fibre has excellent mechanical properties and good thermal stability. However, the use of PBO fibre is limited because of its low photostability. Thus, this work aimed to study the improvement of PBO fibre photostability. Two methods of adhering UV absorbers to PBO fibre surface, namely, coordination bond method and physical adsorption method, were compared. The photo aging results show that the PBO fibres covered by UV absorbers via the coordination bond method were smooth and had no evident particle agglomeration. These fibres showed more improved photostability compared with those covered by UV absorbers via physical adsorption. After 125 h of photo aging, the tensile strength retention rate of PBO fibres covered with UV absorbers via the coordination bond method was still over 90%, which is far higher than that of untreated PBO fibres (approximately 75%).