A multi-air conditioner capable of simultaneous cooling and heating, includes: a first duct connected to a discharge side of a compressor, through which a refrigerant discharged from the compressor passes at the time of cooling operation; a second duct diverged from the first duct, through which a refrigerant discharged from the compressor passes at the time of heating operation; and an oil accumulation preventing portion formed at a certain section of the second duct to have a height difference, for preventing oil, which is introduced to the second duct from the compressor together with a refrigerant, from being accumulated in the second duct. Accordingly, the multi-air conditioner capable of simultaneous cooling and heating can prevent damage to the compressor due to a shortage of oil and thusly improve reliability of a compressor by preventing oil accumulation within a duct.