Civil Service sick pay in Northern Ireland is at its highest level for four years, according to the latest finance department figures.
DSD staff take an average of 18.7 days a year off sick
The figures were disclosed in response to a written question tabled to the Finance Minister Peter Robinson.
DUP MLA Stephen Moutray said the £25.5m cost was the equivalent of more than 300,000 working days in a year.
The public service union Nipsa said a number of civil servants worked in a stressful environment.
Mr Moutray said the sickness levels differed between departments, with the Department of Regional Development averaging 10 days per employee per year but the Department of Social Development averaging 18.7 days.
"MLAs are charged to ensure we get good value for money on behalf of the tax-payer," he said.
"Steps need to be taken across all departments to drive these figures down urgently."
John Corey from Nipsa said the figures used to compile the sickness levels were "skewed".
He said civil service short-term sick leave was no greater than that in the private sector.
Mr Corey said the civil service data included people in long-term sick leave and that in a workforce of 30,000 people there were bound to be hundreds of people who were seriously ill.
He said there was a disparity between the different departments, but the Department of Social Development included front-line benefit staff.
"These are highly stressful jobs," he said.
"We as a trade union have been asking for a very long time for a serious examination of the causes of sick leave and particularly for a full assessment and examination of the levels of stress the civil service feel in their day-to-day work."
Last year, the total cost of sickness amounted to £25,649,986 - in 2003 the figure was £26,110,505.