Potato (Solanum tuberosum L.) is one of the most economically important crops worldwide for both consumers and farmers; however, it is subjected to huge losses as a result of bacterial, viral and fungal attacks. Therefore, genetic engineering is being used to generate potato crops that are resistant to herbicides, insects and pathogens. It is becoming increasingly apparent that the proteins of the plant cell wall play an important role in the defence of plants against pathogen attacks. Recent studies showed that overexpression of an extensin gene in Arabidopsis conferred considerable resistance to bacterial pathogen attacks. The key objective of this work was to transform Solanum tuberosum L. cv. Desiree potato plants with the Arabidopsis extensin atExt1 gene under the transcriptional control of the strong constitutive CaMV 35S promoter. Stable transformation of the potato genotype Desiree with atExt1 genes was achieved by an Agrobacterium-mediated transformation. The current research also studied the defence response of the overexpressed atExt1 transgenic potato plants by infecting them with Pseudomonas syringae DC3000 and Pectobacterium carotovorum pathogens; and, symptom development was monitored. To investigate if the expression levels of the atExt1 gene in transgenic potato lines have different responses to pathogen infection, two lines of atExt1 transgenic potatoes were tested: the high-level overexpressed atExt1 transgenic line (the transgenic H line) and the low-level overexpressed atExt1 transgenic line (the transgenic L line). This analysis of extensin proteins in plant defence responses provided further evidence to their real function. Pathogenesis analysis within the transgenic H lines showed that the formation of disease symptoms was restricted by inhibiting the colonisation of the pathogens compared with both wild-type potato plants and in the transgenic L line. Furthermore, basal defences and signal transduction pathways involved in plant defence were not perturbed in the transgenic potato lines, as shown by an analysis of the expression of PR-1 and defensin genes. These results show that extensin overexpression in transgenic H potato plants limits pathogen attacks. This is the first study to generate the overexpression of the atExt1 extensin gene in transgenic potato plants and to examine the response of these transgenic lines to bacterial pathogen invasion.