Kosugi Tengai (小杉天外, November 7, 1865 – September 1, 1952) was the pen-name of a novelist in Meiji, Taishō and Shōwa period Japan.

He moved to Tokyo in 1886 to attend the English Law College (the forerunner of Chuo University, but soon dropped out to devote himself to writing full-time.

Undeterred, he visited Ozaki Kōyō, who confided to Izumi Kyōka that Kosugi would “never realize his ambition” to become a novelist.

Kosugi attempted to write in a realistic and objective manner, without intruding the thoughts or comments of the author into the story narrative, which was considered rather revolutionary for the time.

Although often compared to his contemporary, Nagai Kafū, Kosugi has been criticized for having two-dimensional characters who meet predictable fates based on family or environmental situations.