In this study, the effect of the dietary supplementation with a novel source oftannins on the gut microbiome of pigs was evaluated. Tannins from differentsources are used in pigs as an alternative to antimicrobials and to zinc and coppersupplementations. This is the first report on the effects of tannins extracted fromtara (Cesalpina spinosa) on the pig gut microbiome. Twenty male finishing pigswere sampled and assigned randomly to the treatment (tannin supplementation)and control groups: rectum swabs were used for 16S rRNA-gene sequencing ofthe gut microbiota. Based on the gut microbiota composition as a whole thetwo groups were clearly distinguishable, as shown by Bray-Curtis dissimilaritiesand by the high accuracy of prediction (0.854) from the OTU-count table with aRandom Forest classification model. On the other hand, other typical indicatorsof microbial diversity, like alpha diversity indices, and the F:B ratio, were notsignificantly different between treatment and controls, likely because of the smallsample size. In conclusion, the dietary supplementation with tannins from taraextracts appears to significantly alter the overall gut microbiome of finisihingpigs, although it is still unclear how this reverberates at the level of specificmicrobiome diversity indicators.