The AuM on CF Miton UK Value Opportunities Fund slipped to £388mln from £783mln by the end of the period.
The fund’s two managers, George Godber and Georgina Hamilton, handed in their resignations back in April.
In total, the company said it had £2.54bln worth of AuM as of 30 June, compared to £2.78bln at the end of last year.
Miton blamed the “particularly unsettled” post-Brexit markets as well as weaker market conditions earlier in the year.
Despite the poor first half of trading, the firm assured investors that it was “well-positioned” for the rest of the year.
The company – which has eight open-ended investment companies, two unit trusts and four investment trusts - highlighted that its average AuM over the first six months was £2.79bln, compared to £2.14bln for the same period in 2015.
“The group is well-positioned with a range of first class funds to deliver performance for our clients and create value for our shareholders,” said managing director Gervais Williams.
The firm was able to boost its cash balances in the first half to £17.4mln, up from the £14.1mln it had in the bank at the end of last year.
It also added that it will put in place a new remuneration structure in the second half of this year, explaining that it “recognises the importance of ensuring the retention and reward for high quality individuals”.
Shares were up 0.93p, or 4%, to 22.18p.