The variability of surface chlorophyll-a (chl-a) distributions in the northwestern coast of Sumatra are important components associated with the phytoplankton biomass that supports and enrich the fishery resources of the region. This study analyzes satellite data-ocean color derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua for a period of January 2003 to December 2015. The results show that the surface chl-a distribution is strongly associated with the large-scale forcing (e.g. monsoonal winds, EL Niño–Southern Oscillation and the Indian Ocean Dipole). On the seasonal time scale, it is shown that the satellite observed surface chl-a concentration during the boreal fall and winter (September-January) is higher than that observed during the boreal summer (June-August). The highest concentration was observed in September which is about 0.2 mg m-3. In contrast to the western coast, the surface chl-a in the eastern coast of Sumatra has excessive concentration around 0,5-10 mg m-3 all year around. In addition, the study also revealed that the anomaly of surface chl-a concentration was observed along the western coast of Sumatra is much higher during the positive IOD (pIOD) and EL Niño events.