The loss came on an increased turnover of £302.7M, up 21% from the previous year.
Osborne chairman Simon Murray said: "While it is disappointing to report a pre-tax loss for the year, this is primarily the result of provisions taken on two contracts.
"We have continued to grow the business with a diverse portfolio of projects and have developed a strong order book. More than 70% of our work now comes from framework agreements and existing clients."
The family-owned contractor refused to identify loss-making projects, but did reveal that its order book for the next twelve months stands at £242.9M. Osborne has also secured more than £200M of work for 2009/10.
Current Osborne contracts include maintenance and junction improvements on the Nottinghamshire section of the M1 and an extension of Gatwick Airport car park.