The number of women on the boards of Australian public companies has remained stagnant, according to a study by the Australian Council of Super Investors (ACSI).

Although the number of directorships held by women increased last year, most new roles were distributed among women who already held board positions.

"The increase this year in the appointments of women to boards is encouraging, but the numbers remain tiny. Almost half of the 40 new appointments are extra directorships for very able women already sitting on ASX 200 boards," ACSI president Michael O'Sullivan said.

"There is a danger that high-performing women directors will become overloaded, as companies seek to recruit senior and experienced directors rather than tap new talent," he said.

The survey, which was conducted by ISS Governance (formerly named RiskMetrics), looked at the board composition of companies listed in the S&P/ASX 100 Index.

In 2009, women accounted for 11.1 per cent of all individuals holding S&P/ASX 100 board seats and 12.1 per cent of all board seats.

In 2008, women accounted for 10.1 per cent of all S&P/ASX 100 directors and 11.1 per cent of all board seats.

Women held just 3.5 per cent of chairperson roles in the S&P/ASX 100 and 4.1 per cent of executive director positions.

Nearly 30 per cent of S&P/ASX 100 companies in the sample had no female directors in 2009, compared with 32 per cent in 2008.

The survey also looked at non-executive director remuneration and found that this continued to increase in 2009, although by lower rates than in prior years.

The average top 100 non-executive chairperson received $442,994 in 2009, up from $439,449 in 2008.

The average non-executive director's remuneration, excluding chairpersons, was up 3.6 per cent to $190,027 in 2009, while a year earlier this remuneration increased by 5.6 per cent.