Amber usually contains inclusions of terrestrial and rarely limnetic organisms that were embedded in the places were they lived in the amber forests. Therefore, it has been supposed that amber could not have preserved marine organisms. Here, we report the discovery amber-preserved marine microfossils. Diverse marine diatoms as well as radiolarians, sponge spicules, a foraminifer, and a spine of a larval echinoderm were found in Late Albian and Early Cenomanian amber samples of southwestern France. The highly fossiliferous resin samples solidified ≈100 million years ago on the floor of coastal mixed forests dominated by conifers. The amber forests of southwestern France grew directly along the coast of the Atlantic Ocean and were influenced by the nearby sea: shells and remnants of marine organisms were probably introduced by wind, spray, or high tide from the beach or the sea onto the resin flows.