The surveyor trade body said rents were pushed up over the three months to October by rising numbers of people looking to rent while the supply of new property onto the rental market dwindled.
RICS put this down to the difficulty people were having securing mortgage finance and the high deposits required by lenders.
Its member surveyors said the rental market remains buoyant, with properties being let very quickly and landlords experiencing very few voids.
The research showed houses are slightly more popular than flats with 33% more surveyors reporting a rise in demand than a fall, the fastest increase in demand since 2008.
New landlord instructions - a good indication of supply to the market - slipped further, marking five consecutive quarters of falling instructions. And respondents reported that difficulty in securing buy-to-let mortgages is holding back many would-be landlords, and a fresh supply of property entering the market.
Meanwhile, renewed falls in the sales market saw fewer existing landlords choosing to sell their property at the end of a tenancy agreement. The proportion intending to do so declined from 4.1% in the three months to July to 2.5%, well below the survey average of 4.4%.
Across the UK, London saw the biggest increase in rental prices, with a net balance of +86 – the highest number in the series history. A turnaround occurred in the North, where the net balance improved from -3 to +23 but all regions are now recording positive readings.
Looking ahead, the outlook for rents over the next three months remains very firm. 34% more surveyors expect rents to rise than fall, with the expectation that rents for houses will increase at a slightly faster rate than for flats.
RICS spokesman, Jeremy Leaf, said: “The lettings sector has become increasingly strong over the past nine months, in contrast to the housing market which continues to slow. Many have turned to the rental market because they fear further price reductions in the housing market, or because they cannot obtain the necessary finance to buy.
“As a result, rents continue to rise with supply failing to keep up with demand. However, there are increasing indications that more landlords are recognising these benefits and looking to add to their portfolios – especially as there has been a rise in the number of providers willing to offer investment mortgages in recent months.”