Attenuated total reflection (ATR) properties and structures were investigated for spiropyran (SP) Langmuir-Blodgett (LB) thin films. The SP LB films were deposited in the dark onto the cover glass evaporated with AE, The mixture of SP, arachidic acid (C20) and octadecane (HC18) were used for the LB depositions. The ATR properties changed with the molar ratios of the mixtures, SP molecules were found to be better packed forming monolayers in the films with HC18 than without HC18. The ATR properties of the films with HC18 exhibited reversible changes caused by the isomerization, but the charge was small because of the small rate of the isomerization of SP molecules. This result also indicates that the samples with HC18 were compactly packed. The ATR properties also changed with the temperature of heat treatment for the SP LB films with SP and photomerocyanine (PMC) forms. The changes of the structures and the optical properties in the SP LB thin films could be evaluated from ATR measurements.