Arima Naozumi (有馬 直純, 1586 – June 3, 1641) was a Japanese samurai lord who was daimyo of Shimabara Domain and head of the Hizen-Arima clan.
Naozumi was born at Hinoe Castle in Shimabara, in 1586, the first son of daimyo Arima Harunobu, who was a Christian.
He married Konishi Yukinaga's niece Marta (マルタ); however, in order to curry favor with Ieyasu, he divorced his Christian wife and married Ieyasu's adopted daughter Kuni-hime in 1610.
Tokugawa Ieyasu ordered a general persecution of all Christians in Japan, and Naozumi immediately gave up his Christian belief, exiled his former wife and secretly killed his two half brothers: 8-year old Francisco (フランシスコ) and 6-year old Mathias (マティアス).
However, he was dissatisfied with the constant revolts and chaos as a result of the Christian persecution and asked the Shogunate to transfer him to Nobeoka in Hyūga Province.