Niwa is a Japanese surname. Notable people with the surname include:

• Niwa clan, retainer clan of the Oda clan during the Sengoku period of Japan (1603 – 1868)
  • Niwa Nagaaki, Daimyō of Nihonmatsu, 1796 – 1813
  • Niwa Nagahide, Daimyō of Shirakawa
  • Niwa Nagahiro, Daimyō of Nihonmatsu, 1868 – 1871
  • Niwa Nagakuni, Daimyō of Nihonmatsu, 1858 – 1868
  • Niwa Nagashige, Daimyō of Shirakawa, 1628 – 1638
  • Niwa Nagatomi, Daimyō of Nihonmatsu, 1813 – 1858
• Akemi Niwa (丹羽 明美, born 1973), Japanese curler, 1998 Winter Olympics participant
• Daiki Niwa (footballer), Japanese footballer
• Hideki Niwa, Japanese politician
• Koki Niwa, Japanese table tennis player
• Mikiho Niwa, Japanese actress
• Niwa Mitsushige (丹羽 光重, 1622–1701), Japanese samurai and daimyō
• Ryuhei Niwa, Japanese footballer
• Shion Niwa (丹羽 詩温, born 1994), Japanese footballer
• Uichiro Niwa, Japanese diplomat and businessman
• Yasujiro Niwa, Japanese scientist
• Yuya Niwa, Japanese politician