Collectively the landlords, who all live outside of the West Lindsey area, were ordered to pay fines, costs and victim surcharges totalling more than £6,000.
They all pleaded guilty to selective licensing offences during a hearing Lincoln Magistrates Court on June 4.
Coun Sheila Bibb, chairman of the prosperous communities committee on West Lindsey District Council, said: “These successful prosecutions continue to demonstrate the council’s commitment to improving housing standards and management within the Gainsborough area.
“All three of these landlords are not from the local area and this should send a clear message to other landlords operating or looking to operate in the area that we will hold you to account in regards to your legal obligations.
“From May this year the council now has additional powers in relation to the issuing of civil penalties for these offences, which will extend our ability to deal with these issues and hold landlords to account.”
Richard Barratt, from Brigg, pleaded guilty to three offences of operating without the required licences in place.
He was fined £179 per offence, ordered to pay costs of £633.47 and a victim surcharge of £30. The court made a collection order in relation to the total costs of £1,200.47.
Mohammed Faruq, 36, of Willowmead Close, Scunthorpe, entered guilty pleas to two unlicensed offences.
He was fined £1,000 per offence, alongside costs of £435.95 and a victim surcharge of £100. The court made a collection order in relation to the total costs of £2,535.95.
And Margaret Lamport, from Liverpool, pleaded guilty to three unlicensed offences.
She was fined £670 per offence and must pay costs of £468.47 and a victim surcharge of £67.
These take the total number of landlords prosecuted for non-compliance under the selective licensing scheme in the Gainsborough area to nine since its implementation in 2016.