Mount Neishi (根石岳, Neishi-dake) is a 2,603m mountain on the border of Chino and Koumi of Nagano in Japan. This mountain belongs to Northern Yatsugatake Volcanic Group.

Mount Neishi is a stratovolcano. This mountain is a part of the Yatsugatake-Chūshin Kōgen Quasi-National Park. Mount Higashi Tengu (東天狗岳), 2,603 m (8,540 ft), is to the north, along the main traverse route of the Yatsugatake Mountain Range, and Mount Nishi Tengu, 2,646 m (8,681 ft), is to the northwest. There is trail from Shibunoyu (渋の湯) to Nakayama Pass (中山峠, Nakayama tōge), through Mount Higashi Tengu, to Mount Neishi. Additionally, there is a trail heading east to Honzawa Onsen (本沢温泉), on the pass between Mount Higashi Tengu and Mount Neishi.

Mount Mikaburi (箕冠山), 2,590 m (8,497 ft), Natsusawa Pass (夏沢峠, Natsu sawa tōge), 2,423 m (7,949 ft), and Mount Iō, 27,603 m (90,561 ft) are located to the south. A lodge, Neishi Sanso (根石山荘, Neishi Sansō), is located on the south side, 15 minutes from the peak.. The lodge is open April to November. ^[1] The main traverse route of the Yatsugatake Mountain Range passes through the summit of Mount Neishi.

• * Shibunoyu Bus Stop (渋の湯バス亭, Shibunoyu basu tei) or Tatsunokanmae Bus Stop (辰野館前バス亭, Tatsunokanmae basu tei) of Alpico Kōtsū from Chino Station

• Mt Neishi (with Mt. Tengu behind) from Mt Mikaburi, March 2024
• The top of Mount Neishi
• Mount Nishi-Tengu from Mount Neishi
• Mount Higashi-Tengu from Mount Neishi
• Neishi Hut from Mount Neishi