A new species of Nanhaipotamon sp. Nov. was found from the west of Xiapu County, Fujian Province in April 2008. Holotype: male, carapace length 28.2 mm, breadth 35.6 mm, thickness 20.4 mm. Allotype, female, carapace length 22.6 mm, breadth 28.7 mm, thickness 20.4 mm. Male first pleopod reached beyond tubercle of abdominal lock, not reaching to suture of sternites 4/5. Subterminal segment was about 2.4 times as terminal segment, inner horn rounded to squarish, and its outer horn pointed to the upper part of abdomen. Morphologically, this new species is distinguishable to the similar species of freshwater crabs, such as N. formosanum, N. nonriense, and N. yongchunense.