Stamps featuring the couple went on sale in London Thursday, a little more than a week before the big day.
Their official engagement portraits appear on the stamps.
Collectors arrived early to buy them on the first day of issue.
"The royal wedding is special and the stamps are obviously a great commemoration of the event," said Ling Kong, who purchased some of the stamps. "I came very early this morning with my friends and we queued outside, so I'm quite happy I've got my stamps."
So far, about 50 miles worth of paper has been used to print the stamps.
Producers say they'll make more if the demand is high.