Buy-to-let lending has seen a 40% increase in the first half of 2012 compared to 2011, figures from Blemain Finance show.
Investment has gradually increased in the last six months for buy-to-let second charge cases, showing landlords are still happy to invest in the market.
The news comes as strict mortgage criteria and house prices increases have pushed more consumers towards renting over buying.
Gary Bailey, director at Blemain Finance, said: "Securing a loan on a rental property is an effective means of raising funds for a variety of reasons, such as renovation of the property or raising the capital needed to place a deposit on another buy-to-let property.
"By the owner releasing equity in their current buy to let property they can use the funds as the deposit on their next buy to let purchase. This is useful, for example when buying at auction."