A polymer containing photochromic moieties is obtained by means of the transesterification of poly(vinyl acetate) with 2-phenyl-5-carboxy-1,3-indandione. Upon u.v. irradiation of a solution and film of this polymer a transition to its benzalphthalide form is observed. It is assumed that the photochemical isomerization of 2-phenyl-1,3-indandione can also start from its enol form.