Meiofauna and marine nematode communities were investigated in Pak Phanang Bay, Nakhon Si Thammarat Province during dry season in May, 2007 and wet season in October, 2007. The study area was divided into 17 stations covering mangrove plantations and mangrove waterways on eastern coastline, Pak Phanang River – western coastline of Pak Phanang Bay and the outer part of the bay. Twenty – three taxa groups of meiofauna were recorded. Nematodes and Foraminiferans were the most dominant groups in both seasons. Density of meiofauna ranged from 3 – 2,897 ind./10 cm2. Meiofauna density showed significant differences during two season with highest density recorded during dry season. Marine nematodes of 63 species from 55 genera 22 families were recorded from the area. These nematodes were common in organic-enriched condition. The density ranged from 1 – 2,863 ind./10 cm2 with high density in the mangrove plantations and outer part of the bay. Rich diversity indices in the range 0-3.14 were recorded with the highest in the mangrove plantations and lowest in the Pak Phanang River. The dominant marine nematodes found in mangrove plantation area with rich organic detritus deposition were mainly epigrowth feeders and selective deposit feeders. These nematodes were mainly with small buccal cavity and with fixed teeth. Amphid found on these nematodes were usually spiral type with a single turn and circular type. The body wall were usually striated. Desmodora sp.1, Perspiria sp., Terschellingia c.f. longicaudata and Haliplectus sp. were among the dominant marine nematodes found in mangrove plantations area. T. c.f. longicaudata was the dominant marine nematodes in the mangrove waterways. These marine nematodes feed similarity to these found in the mangrove plantations being epigrowth feeders and selective deposit feeders. In organic-enriched area due to organic pollution from domestic wastes, fishing piers and aquaculture as in the Pak Phanang River, high diversity of marine nematodes in term of buccal cavity and feeding types were recorded. Predatory and omnivorous marine nematodes were common. Various body wall types were found such as smooth, striated, dots and marked with longitudinal rows of structure. Parodontophora sp. and Gomphionema sp. were the two dominant nematodes in the Pak Phanang River. The non-selective deposit feeders, Metalinhomoeus sp. was common in the outer part of the bay. Marine nematode can be used as pollution indicators. Marine nematodes communities in Pak Phanang Bay indicated the organic-enriched condition in the bay. Desmodora sp.1 and T. c.f. longicaudata were proposed as indicator species of organic-enriched condition. Organic pollution index, the ratio of nematodes to copepods of greater than 100 indicated the disturbances in the Pak Phanang Bay in particularly the mangrove plantations eastern coastline, Leam Thalumpuk and Klong Pak Phraya. High density of the two nematode indicators in the mangrove plantations were observed. The maturity index, which was the ecological measure of environmental disturbance based on nematode species composition, revealed the high disturbance area in the mangrove waterways and Pak Phanang River due to domestic pollution and physical disturbances when compared to the mangrove plantations and outer part of the bay.