Police are appealing for information after a man managed to gain entry to the property on Fells Rigg, Livingston around 6.45 pm on Saturday.
He assaulted the 82-year-old resident before making off with the money.
He has been described as white, around 5ft 10in tall, medium build and in his late 20s.
He had untidy brown hair, was clean shaven, spoke in a local accent and was wearing a jacket and trousers.
The victim did not require hospital treatment.
DS John Bowerbank said: “This was a reprehensible attack on a man within his own home and we are working to identify the man responsible.
“We would urge anyone who may have seen any suspicious activity or who recognises the man descried to get in touch.
“Anyone who can help can call 101, quoting incident 3369 of 6 November."