The cyclopoid copepod Macrocyclops fuscus is distributed in Hokkaido, Honshu, and Kyushu in Japan. The present study revealed that the nauplius insters of M. fuscus are easily collected from ovigerous females on several days without food, indicating the possibility that the nauplius instars of M. fuscus becomes a good teaching material. The first and the thire nauplius insters of Macrocyclops fuscus are described. They bear the antennae 1 and 2, and the mandible. It was suggested that the difference of the armature and the morphology of the antennae 1 and 2 take part in the swim function by the comparison with an unidentified calanoid copepod.