Fishery biology of Loligo duvauceli in the lower Gulf of Thailand covering fishing areas of changwat Nakhon Si Thammarat, Songkhla, Pattani and Narathiwat was studied. Samplings were divided into 2 parts. The first part consisted of random sampling of catches from middle size otter trawlers (boat length 14-18 m) at main fishing ports by marine fishery scientists during January 1994-December 1995. The second sampling periods were done at the port of Songkhla from middle size other trawlers (boat length 14-18 m.) during January to March and July to September 1997 which were considered the spawning peaks of squid. The estimated asymtotic length (L) were 24.9 cm. and 23.3 cm. while curvature parameter (K) were 1.4 yr-1 and 1.6 yr-1 in male and female respectively. The intial condition parameter (t0) were -0.004 yr in both sexes. The total mortality coefficients (Z) were 3.97 yr-1 and 8.70 yr-1 in male and female. The natural mortality coefficients (M) were 1.42 yr-1 and 1.58 yr-1 whereas fishing mortality coefficients (F) were 2.55 yr-1 and 7.12 yr-1 in male and female. Exploitation rate (F/Z) were 0.64 in male and 0.82 in female. The result showed that male and female squid were overfished by 32% and 70% using maximum sustainable yield (MSY) as a reference point. Reducing exploitation rates of both sexes to 0.5, male and female squids were still overfished by 27% and 55%, respectively of both sexes to 0.5, male and femal squids were still overtished by 27% and 55%, respectively. Combining sexes, squid was overfished by 50% and 40% at the present exploitation rate and at 0.5. Ratio of mature female to total female categorized by length class described by a Johnson Schumacher function and a logistic curve revealed that the calculated lengths at first maturation was 8.46 and 8.47 cm., respectively. The relationship between fecundity and mantle length could be described by a power function. Peaks of spawning were observed prominently in March to April and October. To allow squid to spawn, length at first capture should be set at 9 cm. by changing mesh size from 2.5 cm. to 3.5 cm. If the exploitation rate was maintained at the present rate, the higher MSY would be achieved by reducing fishing effort by 10%. To obtain maximum sustainable economic yield (MSE); however, fishing effort should be reduced by 45%