Novel 1-[beta-(4-trifluromethyl benzoyloxy)ethyl]-3, 3-dimethyl-spiro[indoline-2, 3’-[3H]-naphtho[2,1-b]-1,4-oxazine](III) was prepared and their photochromic properties were investigated in polystyrene (PS) films. It is shown that the kinetics of thermal decoloration was decreased with increasing concentration of III in PS films.