The cost to the taxpayer fell in 2012-13, while running costs and staff numbers are also down, according to the board's annual report.
Chief executive Lindsay Montgomery said: "Although some grants of legal aid can attract negative public or media attention, legal aid provides people with important help at vulnerable times in their lives. It is also there to pursue cases in pursuit of the public interest, such as clarifying new areas of law.
"But the fact remains that even after the savings that have already been delivered and the savings that we expect to deliver in future years, the level of legal aid expenditure expected in the next two years is above the Scottish Government's spending plans.
"Substantial additional reform of the wider justice system is also planned, which will impact further on legal aid expenditure."
Savings must be found while protecting access to justice, he said.
Money from the Government to meet running costs has been reduced by 26% in real terms since 2007 and a further drop is planned. Staff numbers have been cut by 12% over the past three years.
At the same time, the board expects workloads to increase, including an expected 20,000 applications for children's legal aid as a result of changes to the children's hearings system.
The annual accounts show expenditure on the legal aid fund was £150.2 million, which is about £7.4m lower than the previous year.
Civil legal assistance spending fell by 9.1% to £49 million, while applications increased by nearly 4%.