A procedure for the spectrophotometric quantification of thiosens in a new lyophilized liposomal drug form containing lecithin, cholesterol, and PEG-2000-DSPE at a molar ratio of 1:0.22:0.002 in addition to sucrose solution (cryoprotector) at a lecithin:cryoprotectant mass ratio of 1:2 was developed. The influence of excipients on the analytical results and the observance of the Bouguer-Lambert-Beer law was evaluated.