The present invention provides aBifidobacterium lactisGKK2, a composition comprising thereof and its use for improving allergic asthma, especially, for decreasing airway resistance, reducing level of non-specific IgE in serum, reducing level of specific IgE in serum, relieving bronchoconstriction, and increasing level of GSH reductase in tissue fluid of liver to improve allergic asthma.本發明提供一種乳雙歧桿菌GKK2、含其之組合物及其改善過敏性氣喘之用途,用於降低呼吸道阻力、降低血清中非特異性抗體IgE含量、降低血清中特異性抗體IgE含量、減緩氣管收縮程度及提升肝臟組織液中穀胱甘肽還原酶(GSH reductase)之含量,以改善過敏性氣喘。