A positive crankcase ventilation (PCV) system includes: an oil separator separating oil from blow-by gases; a PCV valve allowing the blow-by gases from which the oil has been separated by the oil separator to flow into intake ports of a cylinder head; a PCV passage vertically extending from the PCV valve; a PCV chamber connected to the PCV passage; and a plurality of bypass passages branching off from the PCV chamber to the intake ports, respectively.