More than £16,000 worth of high powered tools were stolen during a raid in Great Harwood.
Burglars targetted the building and construction firm S &J Developments on Sunday.
Police said they broke in through the fire door some time after 3pm before escaping with one of the firm's vans which had been loaded with tools.
The thieves later ditched the van nearby and switched the tools to another vehicle before fleeing.
Scott Mitchell said the incident has damaged the business, which is run by his mum and dad Janet and Steven Mitchell.
The 24-year-old, who was running the place while his parents were on holiday in Spain, said: "The tools have been acquired over a great number of years. We are going to have to hire the goods as and when we need them now. We are just going to have to get by because the tools aren't coming back. It's damaging because we have been done over."
Janet Mitchell, 45 and Steven Mitchell, 46, have run S &J Developments on Union Court for 20 years.
A spokesman for Lancashire Police said an investigation is ongoing.