The retinoic acid receptor-related orphan receptor γt (RORγt) is a key regulator of Th17 cells, associated with autoimmune diseases, making it a significant drug target. Herein, we designed and synthesized 1-(phenylsulfonyl)-1,2,3,4-tetrahydroquinoline derivatives, improving upon GSK2981278 to enhance bioavailability. Of which, D4 exhibited superior bioavailability (F = 48.1 and 32.9% in mice and rats, respectively) compared to GSK2981278 (F = 6.2 and 4.1%, respectively), and effectively treated psoriasis in mice at lower doses. Moreover, for the first time, we report the efficacies of a RORγt inverse agonist in mouse models of rheumatoid arthritis. (R)-D4, the eutomer of D4, matched or exceeded GSK2981278's therapeutic effects at lower doses, with no adverse effects observed after 2 weeks of administration. These results position (R)-D4 as a promising and orally bioavailable candidate for Th17-mediated autoimmune disease treatment.