Royal Mail is raising the price of a basic second class stamp from 20p to 21p on 1 April.
In real terms, stamp prices are lower than they used to be
The price rises come just as its German competitor Deutsche Post World Net enters the UK.
It is the first time Royal Mail has raised stamp prices since May last year when prices went up by a penny.
The price of a basic first class stamp will remain unchanged at 28p while other first class post will be cheaper.
"The price of a basic first class stamp will still be 4.5% lower than 5 years ago in real terms," Royal Mail said.
Basic second class stamps are 6.1% cheaper in real terms, the company added.
Airmail to Europe will also become more expensive, as will standard parcel post within the UK.
Deutsche Post World Net, which includes the courier company DHL, said that it has gained access to Royal Mail's UK delivery network.
Deutsche said it has been granted a long-term operating licence by Postcomm, the national postal regulator.