More than 4,000 people in the borough should have received a letter on how to renew their Freedom Pass before the expiry date on March 31.
People can do this online in a few minutes or for anyone who needs guidance applying can head down to their local libraries for help.
Alternatively, the form attached to the renewal letter can be returned by post.
The Freedom Pass can be used on most public transport including trams, buses, tubes, Overground, DLR and National Rail (within the pass boundaries).
Councillor Kamaljit Kaur, cabinet member for adult social care and health services at Hounslow Council, said: “Anyone whose older person’s pass expires on March 31 this year is entitled to a new one, provided they still live in London.
“New passes can be used as soon as they arrive, there’s no need to wait for the old ones to expire. You should destroy the old pass when your new one arrives.
“If you have changed address within London and not informed the Freedom Pass helpline, please do so to ensure the letter is sent to the correct address.”
If your pass expires in March but you have not received a renewal letter contact London Councils via www.freedompass.org or call 0300 330 1433.
Pass holders whose passes do not expire on March 31 2016 do not need to do anything as part of this process.