Arai Kentarō (荒井 賢太郎, 25 November 1863 – 29 January 1938) was a politician and cabinet minister in the pre-war Empire of Japan.

After graduating from Niigata University, he worked for a period as an elementary school teacher.

His classmates included the future Prime Minister of Japan, Wakatsuki Reijirō and President of the Permanent Court of International Justice Mineichirō Adachi.

In 1892, he accepted a post in the Ministry of Finance, rising to head the Budget Bureau.

Arai resigned his seat in the House of Peers in October 1926 and was appointed to the Privy Council.