A rare case of the dental anomaly, viz., intranasal tooth was observed in a female Japanese macaque monkey (Macaca fuscata) (K-105) from Kinkazan Island, Miyagi Prefecture in northeastern Japan. Intranasal tooth is an ectopic tooth erupted into the nasal cavity. The intranasal tooth of K-105 is a left P⁴ based on the morphology, and is not a supernumerary tooth. Intranasal tooth is one symptom, but, its etiology may be divided into two; one is the problem of tooth germ's development that causes intranasal teeth as supernumerary teeth, and another is the problem of tooth germ's migration that causes intranasal teeth as missing teeth from the dentition. In our sample, the tooth germ of the left P⁴ probably moved from the normal position to the nasal floor in an early life stage and developed there. The crown proportion is different from the typical P⁴ in the Kinkazan specimens. K-105 has relatively short buccolingual breadths of P⁴ on both sides. The intranasal tooth may have been an obstacle to breathing to some extent, yet K-105 survived until adulthood. The disadvantage of having an intranasal tooth in this case was not serious.