Sepia dubia is a species of cuttlefish native to the southeastern Atlantic Ocean. It is known only from the type locality, where it was caught at a depth of 25 m. S. dubia is known to grow to a mantle length of 17 mm. The type specimen was collected in False Bay, South Africa (34°11′S 18°27′E / 34.183°S 18.450°E). It is deposited at The Natural History Museum in London.