The bank lent £730m between July and September, up £53m from the £677m completed in the same period last year.
Its net loan book also grew by 16% in the nine months to September – up £1.18bn to £8.5bn compared to the same nine months last year.
An OSB spokesman told Specialist Lending Solutions that the commercial and bridging operations were doing particularly well.
He added that the asset finance arm was beginning to see business volumes grow but it is still new and not a significant contributor to income yet.
The second charge market remains competitive but OSB said it was comfortable that the lending it was doing remained appropriate for the risk involved.
Overall the lender expects net loan book growth of around 20% for the full year in 2018.
One Savings Bank CEO Andy Golding said he was pleased with the continued performance of the bank.
“We delivered 16% net loan growth in the first nine months of the year and entered the fourth quarter with a strong pipeline, enabling us to increase our full year guidance for net loan book growth to c.20%,” he said.
“Our lending and retail savings franchises continue to perform very well. Current levels of applications in our core buy-to-let and commercial businesses remain strong and we are building a robust pipeline for Q1 2019.”
Golding added that while there was an uncertain macroeconomic outlook, he believed the bank’s position and stress tests meant it would be prepared for a potential downturn.