The venture combines the strengths of IMS' global pharmaceutical and consumer health expertise with Nielsen's worldwide experience in fast-moving consumer goods.
It will offer clients a series of new services that will deliver integrated views of pharmaceutical product performance in Japan, including prescription and OTC activity - within a product category.
The alliance will also develop value-added information and consulting services for the country's consumer health industry.
Lennart Bengtsson, ACNielsen Japan managing director, said the move would provide clients with "fresh insights to support their marketing and sales decision-making in Japan".
The aim is to give pharmaceutical and consumer health players the analytical tools to more effectively manage their marketing mix and brand performance and optimise their sales resources.
The IMS/ACNielsen partnership in the country is part of a broader global alliance between the two organisations, which extends to other major consumer health markets in North America and Europe.