The consultancy has bought Newark-based Burks Green - one of the largest industrial architecture firms in the UK, with a £13.6m turnover.
At 190 strong, the business, which also employs many engineers, specialises in infrastructure, factory and airport architecture. The deal is worth £21.2 million.
The takeover comes two years after RPS snapped up Birmingham's Mason Richard Partnership.
It is further evidence that RPS, which is one of the top three planning consultancies, is committed to the architecture market for growth opportunities.
Alan Hearne, CEO of RPS, commented on the deal: 'The acquisition of Burks Green is excellent news for RPS.
It augments the group's skills with expertise much in demand and which will ensure we remain positioned as market leaders in the planning and development sector.
'The well-respected directors of the company will all be remaining with the business.
'We anticipate announcing strong results for the first half of 2006. Burks Green will help us sustain both our operating margins and growth.'