Siamese contact with Japan might be traced back to the end of the fourteenth century when an Ayutthayan royal envoy to the Korean court reportedly made a one-year stay in an unidentified place in Japan before reaching the Korean capital in 1388. There are a few more references in Korean sources to the visits of Siamese envoys, who might or might not have touched Japanese soil before they reached the Korean capital. These records of sporadic Siamese contact with Japan, however, do not necessarily imply that the Thai ever entertained an idea of opening trade relations with Japan in those early years.

The earliest commercial contact of the Siamese with Japan was made not directly but through the intermediary of the Ryūkyūan merchants, who seem to have started their visits to Ayutthaya in the first decades of the fifteenth century. They exported to Ayutthaya such Japanese products as swords and paper fans in exchange for Siamese sappanwood and pepper, which were eventually brought to China as their tribute, whereas the Japanese swords, as is widely known, were cherished by the Siamese royalty as part of their indispensable regalia. Thus, thanks to the Ryukyuan traders, Japan had been known to the Siamese, by the fifteenth century at the latest, as a producer of swords as well as refined fans.

Starting in the beginning of the next century, the Iberians began their religious-military expansion toward Asia. The Portuguese, who occupied Malacca in 1511, sent their envoy to the Siamese capital of Ayutthaya in the following year.