A novel series of 1,2,4-thiadiazole compounds was discovered as selective S1P(1) agonists. The extensive structure-activity relationship studies for these analogues were reported. Among them, 17g was identified to show high in vitro potency with reasonable free unbound fraction in plasma (F(u) > 0.5%), good brain penetration (BBR > 0.5), and desirable pharmacokinetic properties in mouse and rat. Oral administration of 1 mg/kg 17g resulted in significant peripheral lymphocytes reduction at 4 h after dose and rapid lymphocytes recovery at 24 h. 17g showed a transient lymphopenia profile in the repeated dose study in mouse. In addition, 17g also demonstrated efficacy comparable to that of FTY720 (1) in the mouse EAE model of MS.