The move is part of a consolidation project to move all web hosting to a single provider to improve security, scalability and stability.
Aviva is the world's fifth largest insurance group and the largest insurance provider in the UK with more than £364bn of assets under management.
With a significant proportion of Aviva's £41.5bn in premium income and investment sales processed via its many websites, maintaining a stable and secure web presence is a priority, said Aviva.
Christian Fowler, senior technical authority at Aviva, said, "The decision to move to a single provider was sparked by the acquisition of RAC in 2005. The new secure architecture provides Aviva with real stability for our commercial sites which is vital as they process millions of pounds per month in transactions.
"With NTT Europe Online we can also quickly scale up in capacity if needed to handle large traffic spikes to keep the sites online and maintain a quality customer experience."
With NTT Europe Online, Aviva now has three hosting areas in place - a production and testing environment for new sites and services, a disaster recovery site, and the live system where the sites are delivered to the public.
In addition to hosting the group's websites, NTT Europe Online is also working with Aviva to develop and host the company's dedicated internal systems.
Fowler said, "NTT Europe Online is also hosting our extranet available to Aviva employees across the globe. It's an integral part of our internal communications, so ensuring it is always available to employees and partners is of the utmost importance to the business."