The natural autoxidation of thujopsene 1 afforded three dimeric peroxides (14,15, and 16) as the major products. 9α,10-Epoxy-8α-thujopsanol 17 was separated as a minor product besides other known compounds, allylic alcohols 2 and 3, mayurone 7, thujopsane-8α,9α-diol 11, and thujopsan-9-ones 19 and 20.