The detection of hepatitis B virus surface antigen (HBsAg) with the use of a model IAsys+ two-channel optical biosensor is based on the registration of interaction between anti-HBs monoclonal antibodies forming the surface layer of the biochip of the biosensor cuvette and blood serum HBsAg. For the first time a two-channel optical biosensor has been used for the detection of HBsAg in blood serum samples. The comparative analysis of the detection of HBsAg by two methods, viz. with the use of an optical biosensor and the enzyme immunoassay, has demonstrated lower sensitivity, but higher specificity of the detection of this antigen by means of a model IAsys+ biosensor with the biochip, prepared in the process of the work. The main advantages of the biosensor detection lie in the registration of interaction in real time without introducing special markers into the molecules under study.