Archaeological excavations in Yenikapi revealed valuable information about the ship building techniques in Byzantine period. The purpose of this study is to perform wood identifications of the 27 trade ships of Yenikapi and to discuss and compare the wood use from 6th to 11th century. Using standard wood identification techniques, 3122 wood samples from 27 trade ships were identified. Wood identification revealed these important outcomes: Wood use changed from earlier time (5th - 6th) to later (7th - 9th and 10th - 11th). During 6th-8th centuries generally conifer woods were preferred. Later, during 9th - 11th broad-leaved trees (elm, oak, chestnut species) had been used. The reasons of this change may be (1) preferring more resistant woods, (2) obtaining of the wood material. Wood identification showed that the origin of the ships might be around of the Marmara Coasts and northern forests. Conifer trees in earlier ships might be from the planted areas by the Bosporus, and broad-leaved trees in later ships might be from the northern forests. Most of the ships have also very low number of different woods such as walnut, poplar and hornbeam. These woods may indicate some small repairs in the ships.