Boyd Coughlan provides advice to corporate and personal clients and has £160 million of assets under advice.
Mattioli has also announced plans for raising £18.6 million through a share placing to help it “take advantage of further acquisition opportunities”.
Boyd Coughlan's management team will be retained by Mattioli.
In a statement to the stock exchange, the company said its acquisition provides the group with a wider audience for its products and services.
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The deal extends the group's employee benefits proposition “at the time when the drive towards total reward and flexible benefits is expected to create new business opportunities in the corporate market”.
Ian Mattioli, chief executive of Mattioli Woods, said: "Boyd Coughlan is an excellent strategic fit, offering real synergies with the wider group. The acquisition gives us the ability to offer our pension, property and investment products to Boyd Coughlan's clients and to offer enhanced employee benefits services to Mattioli Woods' clients, strengthening our market position.
"It is our ambition to continue expanding Mattioli Woods' operations both organically and by acquisition. All our acquisitions completed to date have been earnings enhancing and have broadened or deepened the Group's expertise and services. Raising capital now will give us the flexibility to pursue both existing and new acquisition opportunities as they arise."
The company announced a trading update today as well, showing total client assets under management, administration and advice had increased over the year by 17% to £5.4 billion at 31 May 2014, of which discretionary assets under management accounted for over £1 billion.
It said that it had seen strong growth in its core pension and wealth management business, with the pension freedoms creating additional stimulus.
Mr Mattioli said: “I am delighted with the performance of our business in what has remained a rapidly-changing market.
“The Government's pension reforms have repositioned pensions at the forefront of Financial Planning, which together with the continued development of our consultancy team has driven strong growth in wealth management.”
The recent acquisitions of the UK Wealth Management and Torquil Clark pensions businesses are “integrating well”, the firm added.