Primary production and related parameters were studied in the inshore waters of Tuticorin during 1985-87. The annual cycle of primary production indicated three peak periods, first during March-April, second during July and the third during September-October. Production was low in the winter months of November-January. The average primary production was estimated as 350 mg C/m³/day with relatively higher values of 1600 mg C/m³/day in April and low values of 114 mg C/m³/day observed in November. The chlorophyll a values showed a direct relation with the primary production. The hydrological parameters including nutrients of the water column showed definite seasonal fluctuations. The nutrients, especially phosphates and silicates showed an inverse relationship with primary production while nitrates indicated a positive correlation. Blooming of Trichodesmium theibautii during summer (April-June) and of dinoflagellates during northeast monsoon (October-December) were observed to be of regular phenomenon. The important dominant group of phytoplankton encountered in the study belonging to the species of diatoms Chaetoceros, Skeletonema and Thalassiosira and phytoflagellates such as Isochrysii, Pavlova, Chromulina and Dicrateria. The role of environmental factors in the production of organic matter and the observations of earlier workers are briefly discussed.