The Southern Health Trust’s bill for agency staff hit £7.8million in the past year, up from £6.7million in the previous year.
The figures were released by the Department of Health at the Northern Ireland Assembly.
There were similar increases reported by other trusts in Northern Ireland, with the Belfast Trust posting the highest bill at £27million, followed by the Northern Trust at £15.7million. The Southern Trust reported the lowest bill in Northern Ireland.
The rise in spending on expensive temporary staff comes despite trusts being under pressure to cut costs.
Across Northern Ireland, spending on agency staff topped £70m last year, having soared by 60% over the last four years.
In some cases nurses costing as much as £87 an hour were brought in to cover chronic staff shortages.
Critics have accused health chiefs of “squandering” money on temporary workers, and claimed recruiting more full-time staff would provide much better value.
In some cases spending on agency staff has spiralled alarmingly.
A spokesperson for the Southern Trust said: “Agency staff expenditure is kept under review and ongoing efforts are made to reduce spend in this area.”