Aims: The transfer of tetO gene conferring resistance to tetracycline was studied between Campylobacter jejuni strains, in the digestive tract of chickens. Methods and Results: In vitro conjugation experiments were first performed in order to select donor/recipient couples for further in vivo assay. Then, chickens were inoculated with a donor/recipient couple of C. jejuni strains displaying spontaneous in vitro tetracycline resistance gene transfer. The donor was a tetracycline-resistant ampicillin-susceptible strain, and the recipient was a tetracycline-susceptible ampicillin-resistant strain. Chicken droppings were streaked on antimicrobial selective media and bi-resistant Campylobacter isolates were further characterized according to their donor or recipient flaA gene RFLP profile. The acquisition of tetracycline-resistance gene by the recipient C. jejuni strain from the donor C. jejuni strain was confirmed by tetO PCR. Conclusions: The study showed that transfer of tetO gene occurs rapidly and without antimicrobial selection pressure between C. jejuni strains in the digestive tract of chickens. Significance and Impact of the Study: The rapid and spontaneous transfer of tetO gene may explain the high prevalence of tetracycline resistance in chicken Campylobacter strains.