Don Hoi Lot (Thai: ดอนหอยหลอด) is a sandbar off the coast of Samut Songkhram Province at the northwestern tip of the Bay of Bangkok. The sediments of the Mae Klong River together sediments from the sea form a system of mudflats, which is settled by the Razor Clam shell (Solen regularis), which also gave the site its Thai name. The site has the largest population of this shell species, which is endemic to the northern Gulf of Thailand. Also 18 bird and 42 invertebrate species are recorded at the mudflats and the adjoining coastal mangrove forests.
The mudflat Don Nai is located directly at the coast and accessible by car. At Chu Chi village several sea food restaurants offer the local shells; also the highly-revered shrine of Prince Chumphon Khet-Udomsak attracts Thai visitors.
Since July 5 2001 the site is registered as Ramsar site number 1099.