The move comes after Nikon decided to consolidate its media planning and buying into one agency. The business was previously split between a number of agencies, with BLM Media heading the UK brief.
MediaCom is tasked with all 2005 fourth-quarter media activity across a range of products that includes the Coolpix and Nikon digital SLR cameras as well as the Nikon D50.
The business covers eight territories across Europe, including the UK, France, Germany, the Nordic region, Switzerland and Austria.
The appointment is expected to expand to include five other unnamed European territories in March.
Julian Neuburger, MediaCom's executive director of Europe, the Middle East and Africa, said: "We are delighted to be working with the most iconic brand in the camera market and are excited to contribute to the continued success of Nikon in an incredibly dynamic market."
Martina Beckman, Nikon's marketing and communications manager, said: "MediaCom demonstrated a track record of providing innovative solutions in competitive sectors for international businesses such as Nikon's."