A red tide of heterotrophic dinoflagellate Noctiluca scintillans was observed off Kochi (Southwest coast of India) along with a multi species diatom bloom generated by upwelling induced eutrophic conditions during south west monsoon in August 2008. Spread over an area of ea 5 km2 the bloom was recorded as viscous fluid of tomato soup consistency. Noctiluca cell count of 8.1x 108 cells L-1 were recorded from the bloom area. The whole area where the bloom occurred was conspicuously bioluminescent. The percentage composition of N. scintillans and diatoms in the bloom waters were 56.17% and 43.83% respectively. Diatoms were present in high numbers with cell density 6.32x 108 cells L-1. Diatoms were mainly represented by the species belonging to the genera Chaetoceros, Navicula, Thalassiosira, Coscinodiscus, and Nitzschia which were also the main food item found within the Noctiluca cells. Closer observation of the Noctiluca cells revealed that the food vacuoles contained diatom cells and remains of these species. It is implied that the abundance of N. scintillans could be due to the occurrence of its preferred food species