The present invention provides a Lactobacillus fermentum GKF3, a composition comprising the strain and their use, in which the aforementioned Lactobacillus fermentum GKF3, deposited with accession numbers of BCRC 910824 and CGMCC 15203, can increase the levels of dopamine or/and serotonin in brain tissues, thereby improving the symptoms of the psychataxia such as decreased focus.