Abstract: The behavior of antiepilepserine, 3,4-methylene dioxycinnamyl piperidine, on exposing to light was studied. The photochemical product was prepared and identified as the cis-isomer of antiepilepserine by elementary analysis and HNMR. An HPLC method was established for the determination of antiepilepserine and its cis-isomer and was used to study the kinetics of photochemical isomerization of antiepilepserine in methanol solution. In dilute solution, it obeyed zero-order reaction. Whereas at high concentration, it seemed to be first-order but actually still obeyed zero-order reaction. The photostationary states of antiepilepserine in various containers and on exposing to different light sources were reported and the results were explained.