The survey of 450 chief executives by their association showed that on average they work a 47-hour week, up from 45 hours last year, and 80 per cent take work home at the weekends, compared with 70 per cent in 2003.
Chief executives from charities with a turnover greater than £1m work an average of 50 hours a week, while some at smaller organisations work as many as 80 hours a week.
The median salary has increased by 5 per cent to £52,053. This is just 46 per cent of what local authority chief executives and 56 per cent of primary care trust chief executives earn. In charities employing 200-500 staff, they received an average of £67,000, bringing them closer to public sector salaries.
Although 87 per cent of charities are investing in training for their chief executives, a rise of 12 per cent on last year, the median spend is down to £700 from £725.
Gail Scott-Spicer, Acevo's deputy chief executive, said: "Organisations expect more and more from their CEOs without a corresponding increase in the training or remuneration available to them."
This increase in workload, combined with uncompetitive salaries, may explain why 75 per cent of charities experienced difficulties in filling some vacancies.
However, the picture looks brighter for staff elsewhere in the sector.
Around 40 per cent of charities predict their proportion of full-time staff will increase over the coming year, up from 25 per cent in 2003.
This was one of the findings of the 16th Annual Voluntary Sector Salary Survey 2004, published by Remuneration Economics in association with umbrella body, the NCVO. The survey also found that only 6 per cent of charities predict that staff numbers will fall, compared with 18 per cent last year.
NCVO chief executive Stuart Etherington said: "Knowing how to set remuneration and at what level is a core need for voluntary organisations. As the sector becomes more professional and employs more staff, this need will increase."