The tightened regulation is part of the Financial Services Commission's plan to curb speed loans at a time when the government is trying to tackle the rise in heavy debtors.
In a statement, the regulator said it asked money lenders to show clearer warnings on potential defaults in their TV commercials.
The FSC said it will consider revising a law that will eventually ban money lenders from TV ads.
As of the end of 2016, there were about 12,000 loan brokers at some 110 financial firms. The state commission plans to tighten supervision of these businesses.
The regulation came as competition for "easy and fast" consumer lending is intensifying, the FSC warned.
According to a recent report from the office of National Assembly Speaker Chung Sye-kyun, the number of heavy debtors in South Korea stood at about 3.9 million people in June, reflecting growing potential for default risks among desperate borrowers.
The number of debtors who have borrowed money from more than three financial institutions has been on a steady rise. It stood at 3.38 million in 2013, 3.47 million in 2014 and 3.65 million in 2015.
The combined debt of the "multiple debtors" reached some 450 trillion won ($399 billion) at the end of June.
These people generally have simultaneously taken out loans from a bank, a savings bank and possibly private money lenders. (Yonhap)