Linum usitatissimum L. (flaxseed) is emerging as an important functional food ingredient because of its rich contents, namely, α-linolenic acid (ALA, omega-3 fatty acid), lignans, and fiber, which are potentially beneficial for human health. Furthermore, flax or flaxseed oil has also been incorporated as a functional food ingredient into various foods such as milk, dairy products, and meat products. Flaxseed is known to possess antimicrobial activity in vitro and in vivo, but its growth-stimulating effect on lactic acid bacteria is not clear. Hence, the objective of this study was to determine whether crude flaxseed extract stimulated the growth kefir-isolated lactic acid bacteria in vitro. The result of this study showed that Lactobacillus kefiranofaciens DN1, Lactobacillus brevis KCTC3102, Lactobacillus bulgaricus KCTC3635, and Lactobacillus plantarum KCTC3105 treated with 100 μL of crude flaxseed extract showed significantly higher growth than the control treated with 100 μL of water (p<0.05). Based on the results of this study, crude flaxseed extract could be used as a growth stimulator for lactic acid bacteria in various food applications, including production of milk and dairy products.