-The employment of Camellia sinensis L. whole plant extract as food supplement in livestock nutrition has been suggested in order to prevent usual livestock intestinal diseases. The aim of the present research was to test the effects of such plant extract on the composition of pig faecal microbiota. Preliminary in vitro fermentation trials evidenced in mixed pig faecal cultures, supplemented with the tested extract, an increase of total anaerobe (p = 0.02) and aerobe (p = 0.03) bacteria, and a decrease of clostridia (p = 0.04) compared to control cultures. Afterwards we investigated in vivo the effects on piglet faecal microbiota of a diet added with 250 mg/kg of Camellia sinensis whole plant extract. A control diet without the plant extract, but added with antibiotic (sulphadiazine, trimethoprim, and tiamulin) was used for the comparison. Microbiological analyses of faecal samples collected after 60 days of the experimental feeding, evidenced a decrease of clostridia (p = 0.001) and enterococci (p = 0.04) counts in the faeces of animals fed with the experimental diet, compared to those fed with the control diet. These results show that the Camellia sinensis L. whole plant extract is able to reduce the number of some potential pathogenic bacteria in piglet gut and hence might improve animal health.