Emergency services were called to the collision on the A72 Peebles to Innerleithen road at about 11:10.
Three men - aged 87, 71 and 42 - were taken to hospital. The 87-year-old died a short time later.
Police Scotland appealed for any witnesses to the crash, which involved a red Vauxhall Meriva and a silver Honda CR-V.
An 87-year-old man has died after a crash in the Scottish Borders on Saturday morning.