The Edinburgh-based bank is to shut the Paisley Central branch on May 7, meaning its only town base will be in Moncrieff Street, a half-mile walk from the town's High Street.
The shutters came down on its Paisley Eastern branch in Glasgow Road after some 50 years in March last year.
RBS, which is majority-owned by the taxpayer, said it took the "difficult decision" to close the town centre branch in St Mirren Street which has been in existence for decades as the numbers using the branch had fallen "significantly" over the past few years.
It said customers were choosing alternative ways of banking through the internet, mobile phone apps and telephone.
Paisley and Renfrewshire South Labour MP Douglas Alexander criticised RBS for making the move without any customer consultation. A similar criticism was levelled at the bank over the closure of the Paisley Eastern branch.
He has spoken with the taxpayer-owned bank to make it clear he views it as "totally unacceptable".
He said: "RBS has let local people down by its decision to close the central branch.
"Many elderly customers in particular rely on easy access to their branch, but RBS has decided to force this closure upon them. They will have to cross two of the busiest roads in Paisley to get to the next nearest branch. That is not the way to treat loyal customers.
"Rather surprisingly given they have just announced its closure, when I spoke to RBS they were unable to provide me with the full details of how many customers use the branch or how it compares with other branches across the country.
"This closure is even more galling since RBS spend hundreds of thousands of pounds in advertising telling us that it is Scotland's local bank.
RBS said the number of customers using the branch had dropped by 15%
An RBS spokesman said: "More and more of our customers are using alternative ways to bank with us, such as online and telephone banking, or using their mobile phone.
"As a result, we've seen the number of people using the branch fall significantly over the last few years and we've made the difficult decision to close the Paisley Central branch.
"We've advised staff and we're writing to our customers to make them aware of the different ways they can bank with us. If customers are concerned about how this will impact their banking they can go into the branch where staff will be happy to discuss the alternative options available."
RBS had said they had two branches still available in Paisley, Moncrieff Street and a bank in the Piazza Shopping Centre. A Piazza source confirmed the only RBS presence in the centre is an ATM.
RBS also said it had an arrangement in place with the Post Office which allows customers to pay bills, withdraw cash and pay balances.
Paisley has suffered a string of shop closures in recent years as it has struggled to compete against the draw of Glasgow and out-of-town centres.
According to recent data from PricewaterhouseCoopers Paisley has been one of the hardest hit in terms of high street footfall, with 20% of shops empty.