Provided is an oil mist separator capable of preventing separated oil from flowing toward the gas outlet along the bottom surface. This oil mist separator is provided with: a separator body having a gas flow path formed within the separator body; a gas introduction section for introducing blow-by gas into the separator body; a gas discharge section for discharging the blow-by gas from the separator body; a separation means for separating oil from the blow-by gas; dams provided at the bottom wall of the separator body at positions downstream of the separation means and damming the separated oil so that the separated oil does not flow to the downstream side; and an oil discharge section provided upstream of the dams and discharging the separated oil from the separator body. The dams are formed along the gas flow path so as to alternately extend from the pair of side walls of the separator body. The dams extend so that the front ends of the dams are located upstream of the base end sections of the dams and beyond the center of the gas flow path in the width direction of the gas flow path.