Seram is traversed by a central mountain range, the highest point of which, Mount Binaiya, is covered with dense rain forests. Its remarkably complex geology is because of its location at the meeting of several tectonic microplates, which has been described as "one of the most tectonically complex areas on Earth". Seram actually falls on its own microplate, which has been twisted around by 80° in the last 8 million years by the relatively faster movement of the Papua microplate. Meanwhile, along with the northward push of the Australian Plate, this has resulted in the uplift that gives north-central Seram peaks of over 3000 m. On the island are important karst areas. In the mountains near Sawai is the cave Hatu Saka, currently the deepest cave in Indonesia (-388 m). In Taniwell district, on the north coast, is the underground river Sapalewa, one of the largest underground rivers on the planet.
The population of the island in the 2010 Census was 434,113 people, administered among 3 regencies, Maluku Tengah Regency had 170,392 people on Seram Island itself and 191,306 on the lesser islands (majority on Ambon Island), the entirety of Seram Bagian Barat Regency and Seram Bagian Timur Regency.
Seram Island is remarkable for its high degree of localised bird endemism. From the 117 species of birds on the island, 14 are endemic, including the eclectus parrot, purple-naped lory, salmon-crested cockatoo, lazuli kingfisher, sacred kingfisher, grey-necked friarbird and Moluccan king parrot.
The mammals found on Seram include Asian species (murid rodents) as well as Australasian marsupials. The montane area of Seram supports the greatest number of endemic mammals of any island in the region. It harbors 38 mammal species and includes nine species that are endemic or near endemic, several of which are limited to montane habitats. These include the Seram bandicoot, Moluccan flying fox, Seram flying-fox, Manusela mosaic-tailed rat, spiny Ceram rat and the Ceram rat, all considered threatened.