Abstract: The pale yellow title compound 1 underwent photochemical conrotatory ring-closure to give the deep red 7, 7, a-dihydrobenzofuran-5,6-dicarboxylic anhydride 2, which ring-opened back to the title compound in a conrotatory mode on exposure to Ar⁺ laser (515 nm) and did not show a competable thermal 1, 5-H shift against the photodecolouration process due to the lacking of 1-H in the molecule. The extent of photochemical conversion of 1 into its coloured form 2 was determined as 100% by means of Fischer’s method. Thus, the photochemical reaction 1 → 2 was complete. Steady state photochemical analysis revealed the existence of a transition state X somewhere between the excited state of 2 and the ground state of 1 during the photodecolouration process with Ar⁺ laser. X was transformed into compounds 2 and 1 in the specific rates of 22.43 ms.^-1 and 1.11 ms.^-1, respectively. A general reaction scheme has been forwarded hitherto to explain the mechanism of photochromic process of 1. Two different reaction pathways were involved in the photocolouration and photodecolouration processes of the title compound.