Mamiya Rinzo (1844-?) was a Japanese explorer of the late Edo-era.
Mamiya was born in 1775 in Tsukuba District, Hitachi Province, in what is now Tsukubamirai, Ibaraki Prefecture. Later in his life he would become an undercover agent for the Tokugawa shogunate. He is best known for his exploration and mapping of Sakhalin (known to the Japanese as Karafuto), which resulted in his discovery that Sakhalin was indeed an island and not connected to the Asian continent.
In 1785 Japanese explorers reached almost to the Strait of Tartary on the west, Cape Patience on the east and Urup in the Kurils. In 1808 Mamiya sailed up the east coast and Matsuda Denjuro up the west coast. From near Cape Patience Mamiya crossed the mountains to join Matsuda. The next year Mamiya sailed into the mouth of the Amur River and reached a Chinese trading post. In 1852 Mamiya's maps were published in Europe by Philipp Franz von Siebold.
Although Japan believed that Mamiya had no child, it was announced in 2002 that there was a daughter of him and an Ainu woman and her descendants remained alive in Hokkaido.