The man’s actions in the early hours of Friday have been hailed as “heroic” by police.
Emergency services in Paisley were alerted to the flat fire in Tannahill Terrace at around 3.15am.
They were summoned by a 50-year-old man living nearby who had spotted the blaze.
He managed to get into the property and rescue the 64-year-old woman living inside, officers said.
She was then checked over by ambulance staff but did not need to go to hospital.
Police are treating the incident as attempted murder.
Detective Sergeant Ally Semple, of Paisley CID, said: “This was a deliberate, dangerous act and the fast and heroic actions of the victim’s neighbour undoubtedly saved her life.
“Extensive inquiries are under way to establish why someone would have intentionally set fire to this woman’s home and it is vital that the local community support us in finding the despicable individual responsible.”
Police have appealed for anyone who was in the area and noticed anything suspicious to contact Paisley CID on 101, quoting incident number 0347.