An image encoding/decoding method and apparatus are provided. The image decoding method includes obtaining, from a bitstream, network abstraction layer (NAL) unit type information of at least one NAL unit including coded image data, determining at least one NAL unit type of one or more slices in the current picture based on the obtained NAL unit type information, and decoding the current picture based on the determined NAL unit type. The current picture is determined to be a random access skipped leading (RASL) picture, based on the determined NAL unit type including a RASL picture NAL unit type (RASL_NUT). When an intra random access point (IRAP) picture associated with the RASL picture is a first picture in decoding order, the RASL picture is decoded, based on the RASL picture including one or more slices having a random access decodable leading (RADL) picture NAL unit type (RADL_NUT).