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The production of lactic acid (LA) from lignocellulosic biomass is an important route for the exploitation of renewable resources; nevertheless, effective LA production from this feedstock is challenged by several limitations, such as pentose and oligosaccharide utilization. In this study, a new strain, <i>Lactococcus</i> sp. X1, which is capable of fermenting glucose, xylose, and several disaccharides to produce L-lactic acid, was isolated from the gut of a wood-feeding termite, <i>Coptotermes formosanus</i>. Compared to conventional lactic acid bacteria, <i>Lactococcus</i> sp. X1 requires less complex nitrogen sources, which might in turn reduce the cost of LA production. In addition, <i>Lactococcus</i> sp. X1 was able to completely ferment 50 g/L of glucose within 3 days, giving a high LA yield of 99.9%, and its LA yield from 50 g/L of pretreated corncob reached up to 0.34 g/g substrates in the presence of a commercial cellulase. Strain X1 was also capable of excreting two kinds of nutritional factors, namely biotin and vitamin C, indicating its crucial role in the nourishment of the termite. In conclusion, <i>Lactococcus</i> sp. X1 is a new lactic acid bacterium, which may hold promise for application in cost-effective LA production as well as in the field of food additives.