Electrical properties for Langmuir-Blodgett (LB) films of spiropyran (SP) dyes (SP98 and SP1822) and their structure are investigated. SP dyes change from SP to photomerocyanine (PMC) forms as a result of UV irradiation. The UV-irradiated SP dyes change from PMC to SP forms again by visible irradiation or heat treatment. Thermally stimulated current (TSC) measurements are used to examine the electrical properties of the SP LB films. The TSC for the SP LB films is found to be due to the dipolar depolarization. The TSC of the SP98 LB films strongly depends on their structure, and exhibits reversible changes caused by the isomerization. The TSC for the SP1822 LB films, however, does not change clearly as a result of the isomerization. The TSC due to the dipolar depolarization is thought to depend on how the molecules are packed in the LB films. The microscopic behaviour of the molecule may be influenced by its surrounding space.