Three new sesquiterpenes, (−) -tridensone, (+) -aristol-9-en-12β-al and (+)-aristol-9-en-12β-oic acid have been isolated from the liverwort Bazzania tridens, together with the known sesquiterpenoids, (+)-cyclocolorenone and (−)-6S,7S-α-bisabolol. A comparison was also made on the constituents of seven samples of B. tridens samples collected from both Taiwan and Japan.