Wrightbus has increased its turnover by 7% to £168m in 2013.
However, a doubling of spending on research and development saw profits fall back from almost £4m to £1.4m. In total, research and development costs were almost £7m.
The number of people employed at the firm rose over the year from 1,044 to 1,185.
In May, the firm said it was creating a further 130 jobs at its Antrim factory that manufactures chassis. The company is making a total investment of £14m in Antrim - more than £10m of which will be for research and development projects.
The accounts for 2013 state that the 2014 outlook is “encouraging” and that the directors expect an improved financial performance.
The accounts for its ultimate holding company, the Cornerstone Group, also reveal that in September 2012 it spent £2.6m on a property to be used as the group office.