The determination of the elemental composition of plankton is important for interpretation of functional states of the aquatic ecosystems. The present study is focused on the elemental composition of the plankton assemblages from the Atlantic Ocean off the coast of Lagos, Nigeria using scanning electron microscope - SEM (VEGA3 TESCAN) coupled with energy dispersive x-ray spectrometry - EDS (Quantax 200, Bruker EDX) at an accelerating voltage of 5 - 20 kV. Surface plankton samples were collected by horizontal tows with a plankton net (55 μm pore mesh size) at approximately 15 km away from the seashore along the entire Lagos shoreline (180km). The result from the SEM/EDS technique showed that the plankton is composed majorly of 13 elements (O, C, Si, Al, Cl, Fe, Mg, Na, K, S, Ti, Ca and P). The mineral particles of calcium (0.2%), potassium (1.3%), sodium (1.5%), chlorine (5.0%), magnesium (1.8%) and iron (3.3%) as well as organogenic elements of oxygen (36.9%), carbon (27.8%), sulphur (1%) and phosphorus (0.2%) were quantified.