The increase, which is documented in the NCVO's UK Civil Society Almanac 2008 (Third Sector, 20 February), says charities' spending on fund management increased from £88m in 2004/05 to £334m in 2005/06.
Analysis by the umbrella body suggested that a small group of charities were taking investment more seriously and were therefore willing to pay significant amounts in order to ensure good returns.
But fund managers agreed that the move by charities away from stockbrokers to more expensive discretionary fund manager services, plus increased use of sophisticated investment products, had led to the cost rise.
One investment expert, who asked not to be named, told Third Sector: "A push into more specialist areas does need more know-how and monitoring, and that in turn leads to higher fees."
Paul Palmer, professor of voluntary sector management at Cass Business School, said this reflected a trend towards higher weightings in vehicles with higher fees. These included absolute-return vehicles, which seek positive returns whatever the state of the market by using products such as derivatives, and targeted-return vehicles, which use derivatives to produce returns at a target value.
Palmer said: "A good percentage could also be a result of market movement - for example, 0.5 per cent on £1m in 2006 is now 0.5 per cent of £1.1m in 2007."