The material plant of a tinny basket excavated from the San’nai-maruyama site (early Jomon period) of Aomori, Aomori Prefecture, was identified as a stem of a monocotyledon in 1993. On the other hand, a further observation of the basket suggested that the studied material did not derive from the basket. Thus, a newly obtained material of the basket was reexamined anatomically and was shown to be the torn inner bark of a Cupressaceae tree. The original material formerly identified as a monocotyledonous stem was re-identified as a petiole of a fern akin to Arachniodes standishii (Dryopteridaceae). Furthermore, a rope excavated from the Sakuramachi site (middle Jomon period) of Oyabe, Toyama Prefecture, was also made of the same material. These results show that the original sample of the basket was a contamination from sedimentary deposits. This is the first report of a basket made of conifer bark and a rope made of fern petioles in the Jomon period of Japan.