Letting agency Spicerhaart has been fined £2,670 after pleading guilty to operating an unlicensed house in multiple occupation.
A prosecution was brought by Colchester council after housing officers undertook inspection visits at a three-storey property in the town, which was being let to six students.
It fell within the mandatory requirement for HMO licensing as required by the Housing Act 2004 but neither Spicerhaart, operating as the management company, nor the owner had applied for a licence.
Magistrates fined the company £2,000 and ordered it to pay £500 costs and a £170 victim surcharge.
The case against the property owner, who pleaded not guilty, is due to be heard at a later date.
"We hope that bringing this case to court will serve as both a deterrent and a reminder to letting agents and landlords to think twice before letting properties to multiple occupants without an appropriate licence” says a council spokeswoman.