Pterins belong to a family of heterocyclic compounds that occur in wide range of living systems. Photochemical studies of 6-carboxypterin (6-CPT) in neutral aqueous solutions at 365 nm and room temperature were performed. The photochemical properties of 6-CPT are of particular interest because photolysis of this compound takes place in the white patches of patients affected with vitiligo. Folic acid is an essential vitamin which belongs to the conjugated pterin derivatives. Folic acid undergoes photooxidation under UV light to 6-carboxypterin via an electron transfer mechanism from the PABA moiety to the pterin moiety in its excited state. Carboxypterin is reported to further degrade when exposed to UV light. In the current research, photodegradation experiments were performed in phosphate buffered saline (pH =7.3) and in the presence of electron donors in both aerobic and anaerobic conditions (1mM iodide anions, azide anions, and DABCO). The photoproducts were detected by HPLC using 348 nm as the detection wavelength. The rate of photodegradation of 6-CPT was increased in the presence of oxygen but did not much effect the formation of 6-HMPT, however it affected the total amount of the photoproduct formed. Addition of electron donors relatively increased the total amount of photoproduct formed. In all the experiments, the total concentration of the product was not recovered which might account to the formation of non-pteridinic compounds. According to the literature, the missing amount of the product might account to the formation of non-pteridinic compounds. Addition of electron donors decreased the non-pteridinic compounds formed via other pathways. The presence of oxygen increased the formation of non-pteridinic compounds both in the presence and absence of electron donors, indicating an oxidation process involved in the formation of non-pteridinic compounds. The mechanism of the photoproduct formed can be compared to the reduction of nitrobenzene to aniline.