The most widely used probiotic bacteria are lactobacilli and bifidobacteria, which have been isolated from the human gastrointestinal tract. The development of new probiotic strains, which are more feasible and beneficial organisms, is awaited in the dairy industry. Lactococci would be promising species because of their extensive usage in manufacturing dairy products such as cheese and fermented milk. However, there have been few studies on the probiotic activity of lactococci since they are traditionally not considered to be natural inhabitants of the human gastrointestinal tract. Recently, several works showed the possibility of the presence of lactococci in the flora of the human or animal gastrointestinal tract. In this review, we would like to propose Lactococcus sp. as new probiotic bacteria.