Nikken Sekkei Ltd. (日建設計) is an architectural, planning and engineering firm from Japan, with headquarters in Chiyoda, Tokyo.

Today (2019), Nikken Sekkei ranks as the second largest architectural practice in the world.

Nikken Sekkei's International offices are in Tokyo, Shanghai, Beijing, Dalian, Seoul, Hanoi, Ho Chi Minh City, Singapore, Dubai, Riyadh, Moscow, Barcelona; Bangkok; while the Japanese branches are located in: Osaka, Nagoya, Fukuoka, and Sendai.

[2] Nikken Sekkei dates its origins back to 1900, as an offspring of Sumitomo Corporation.

The company established its independence from the Sumitomo Corporation in the 1950s under the name Nikken Sekkei Komu Co. Ltd.[5] As a private practice since 1970, Nikken Sekkei has maintained its In-house Shareholder Corporate System and is partly owned by its employees.