The mass culture of the micro-alga, Chaetoceros gracilis, a live-food for feeding the larval stages of Black Tiger shrimp, Penaeus monodon, was carried out in the in-door shrimp hatchery of Nigerian Institute for Oceanography and Marine Research. Guillard modified f/ 2 medium was used in the production of starter culture and maintenance of the pure algal culture in an indoor laboratory. Mass cultures of C. gracilis were thereafter developed in 1.5 m 3 out-door plastic tanks using Guillard modified f/ 2 medium and Liao and Huang modified medium. The culture reached the stationary phase within 120 hours when exposed to sunlight. Three phases of cell growth of C. gracilis were observed during the culture periods which were lag phase followed by exponential and stationary phases. Average cell density of the out-door culture of the micro-alga was 780,000 cells/mL and the culture remained in this phase for 120-144 hours with a brown colouration. The highest cell density was 1,039,145 cells/mL recorded in the month of October while the lowest was 248,154.7 cells/mL recorded in the month of July. High cell density of the species occurred during the months of January to May and in October. These months were characterized by low humidity and higher temperature. Water temperature and salinity of the mass culture medium ranged from 25-29 o C and 28- 30 ppt respectively. The culture was sustained by semi-continuous culture throughout the study-period which lasted for ten months. The use of enrichment media enhanced sustained continuous culture for all year round alga production. The results obtained in this study indicated that mass culture and all year round production of C. gracilis is feasible in Nigeria.