Four fretting modes exist in ball-on-flat contact according to the direction of relative motion, i.e. tangential, radial, rotational, and torsional fretting. Torsional fretting in a physiological medium is one of the main reasons that artificial joints fail. A new test system was successfully established for torsional fretting in a liquid medium at a constant temperature in a torsional mode with a ball-on-flat contact. The torsional fretting experiments were conducted on Titanium alloys against Zirconium dioxide ceramic balls in a saline solution at 37°C, and the torsional fretting running behaviors and damage mechanisms were discussed in detail. The results showed that the dynamics behaviors were strongly depended upon the torsional angular displacement amplitude and the number of cycles. A running condition fretting map (RCFM) was established, which included 3 fretting running regimes: a partial slip regime (PSR), a mixed fretting regime (MFR), and a slip regime (SR). No damage was observed on the contact center and only slight scratch and wear were observed on the contact edge in the PSR. The damage zone extended to the contact center and the sticking zone (which exhibited no damage) contracted to the contact center with increases in the number of cycles, and some oxidation wear and damage presented on the contact edge region in the MFR. The damage mechanisms were primarily the result of abrasive wear, oxidation wear and adhesion wear in the SR.