Fr Pierluigi Maccalli from Italy was abducted overnight on Monday in southern Niger, close to the Burkina Faso border.
According to one witness, a local nun was also captured in the incident.
While the Italian Government is investigating, the Catholic clergyman's family is praying for his safe return.
Extremists - some aligned to Islamic State or al Qaeda - have been known to operate in the region. Porous borders allow them to move relatively freely between Burkina Faso, Mali and Niger.
A spokesman for Niger's government said the incident marks the second time a European national has been kidnapped in Niger so far this year.
Fr Maccalli, who is 57-years-old and from a small town south east of Milan, was working in West Africa with the Lyon-based Society of African Missions (SMA).
He had spent a number of years working in Ivory Coast before being assigned to Bomoanga, in the diocese of Niamey - a poor district boasting few amenities and little infrastructure.
Fr Maccalli has been working to illuminate harmful cultural practises in the area, including female genital mutilation. There is speculation this might have been one motive behind his kidnapping.
Picture: Niamey Cathedral in Niger
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