Marine bioluminescence is a unique phenomenon and widely studied around the world. However, information on bioluminescence is scarce in the Indian ocean. This study was carried out to understand the spatial and temporal variations in planktonic bioluminescence off the south coast and the Puttalm Lagoon of Sri Lanka. Planktonic bioluminescence intensity, zooplankton samples, water samples and oceanographic data were collected from sampling sites from January to December 2016 in three month intervals. Time series data were collected at a fixed sampling station, off the south coast of Sri Lanka, in order to understand the variation of bioluminescence intensity throughout the night and with respect to monsoon winds. Bioluminescence intensity was measured using the recoverable bathyphotometer and zooplankton samples were collected using WP-2 net with a 180 μm mesh size plankton net. The results revealed that most of the bioluminescence intensity peaks in the ocean were concentrated in the mixed layer depth zone. Bioluminescence and Chlorophyll profiles indicate the presence of both heterotrophic and autotrophic planktonic bioluminescence. Fixed station analysis showed variations in planktonic bioluminescence throughout the night and with respect to monsoon winds. Twenty two surface bioluminescent zooplankton species belonging to 15 families and 4 phyla were identified during this study. Variations in planktonic bioluminescence with respect to time and sampling locations were evident. The current study yielded encouraging results that should lead to further identification of planktonic distribution near Sri Lanka and key bioluminescent zooplankton in the region.