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Campylobacter jejuni is recognized as the leading cause of bacterial enteritis worldwide. Although it is considered as a fragile bacterium, it is able to survive to various stress encountered from the gut of its hosts (mammals, birds, humans) to processed foods, such as cold stress (4°C) or oxidative stress. Ingestion of contaminated food can induce enteritis in consumer, and rarely lead to serious complications such as neuroparalythique syndrome Guillain-Barré. In many bacteria, adaptation to changing environments involves a posttranscriptional regulation achieved by ribonucleases such as polynucleotide phosphorylase (PNPase). This work aimed at studying the involvement of PNPase in biological functions of C. jejuni. Initially the pnp gene encoding PNPase was inactivated by insertional mutagenesis. Inactivation of PNPase significantly reduced survival of C. jejuni at refrigerated temperatures (4 and 10°C), whereas at optimal temperature the two strains have the same behavior. Moreover, PNPase deficiency results in a significant reduction of adhesion and invasion abilities of C. jejuni to epithelial cells and colonization of the avian cecum. Despite an effect of pnp mutation on the bacterial proteome, proteomic analysis revealed that few proteins varied between the wild type and the mutant strains. Further studies should be developed to clarify interactions involving this ribonuclease in C. jejuni survival and virulence.