Apoplastic invertase is the key enzyme of carbohydrate metabolism in plants. The application of transgenic plants, which possess genes of heterologous organisms, expands understanding of the functional role of products of these genes. The purpose of this study was to characterise the invertase of S. cerevisiae from transgenic potato plants (Solanum tuberosum L., cv. Désirée), which expressed the suc2 gene of yeast under the control of the patatin class I B33 promoter. The suc2 gene presence in the plant genome and its expression were shown using PCR and RT-PCR. Yeast invertases were identified by MALDI-TOF MS analysis. Our results demonstrated the transit of the mature protein of the yeast invertase to the apoplast. A soluble form of the yeast invertase was present in the apoplast, and it was weakly adsorbed onto the cellular wall. Glucose and fructose levels in the apoplastic fluid of the transgenic plants increased by 40-55% as compared to those in the wild-type potato plants. Increased acid invertase activity in the transgenic plant leaves was observed as the result of the suc2 gene expression. Moreover, the increased total sugar contents in the transgenic plants led to some changes in their morphometric parameters (decreased offshoot length, less developed root system, and larger water content in tissues). The potato line with the integrated suc2 gene is a convenient tool for studying the role of the apoplastic invertase and the products of its activity in plant growth regulation and adaptation to unfavorable environment (in particular, to hypothermia).