As a kind of rig-rod-like polymer, poly(p-phenylene benzobisoxazole) (PBO) has received great interest because of its excellent mechanical properties and good thermal stability. The use of PBO materials, however, is limited due to its low sunlight stability. In this study, photolysis of PBO films was studied by infrared spectroscopy and molecular mass determination. It found that at the beginning of photolysis, the I.V. values of PBO almost did not changed. Then, it underwent fast decrease stage. Moreover, PBO degrade slowly in N2 atmosphere than in air atmosphere. The most likely photo-degradation mechanism was put forward. Attempts to stabilize PBO from photolysis were also investigated. It found that heat treatment could alleviate photo-degradation speed of PBO. Traditional light stabilizers showed a marginal effect on photolysis of PBO, whereas ferrocene dimethanol behaved better effect on the photo-stabilization of PBO.