Koan Ogata (1810-1863), a medical doctor in Osaka, is renowned for his contribution to the spread of vaccination and for his private school Teki-juku, a Rangaku school where education of Western learning was done by means of the Dutch language. In many letters collected in "Ogata Koan no Tegami" (1980-1996), he asked help for obtaining various Dutch scientific books to his former students, Shuhei Mitsukuri and Ryotei Takeya during several years around 1859: Mitsukuri was a staff member of the Foreign Affairs and intermittently Bansho Shirabesho (Institute for Western Learning) of the Tokugawa Shogunate in Edo, while Takeya was a medical doctor of the Fukuoka Clan. Moreover, Ogata wrote to Mitsukuri in 1858 that he had asked Yukichi Fukuzawa in Edo to buy a Dutch wordbook for him. On the other hand, Genki Kusaka, a student at the Teki-juku, noted in a letter to his parents in 1854 that Ogata had bought Dutch books from Tsuji, official Dutch interpreter of Nagasaki, when the Tsuji stopped by in Osaka on the way to Edo in the February of the year. This paper outlines the above letters to show how Koan Ogata tried to obtain Dutch books from Edo and Nagasaki; their titles and areas are discussed in view of the history of Western learning, and identification is made on the two books that have been left unclarified.