A host of international names have created small works of art which will be displayed anonymously and can be bought for as little as £35.
The popular show gives art lovers a chance to buy a rare work of art but buyers do not find out the identity of the artist until after the postcards have been sold.
The bulk of the cards are painted by students at the London school.
Camping out
Even a postcard by a student is not to be dismissed - graduates of the RCA include Tracey Emin, David Hockney and Barbara Hepworth.
Sir Christopher Frayling, rector of the Royal College of Art, said: "RCA Secret is a unique experience.
"The variety of postcards is astounding, from paintings to photographs, collage to drawings, all in miniature format.
"So this has become one of the largest and smallest exhibitions of contemporary art in the world. It is a fun and creative way of raising money for the students."
Thousands of art lovers often besiege the RCA with many people camping out overnight to ensure their place at the head of the queue.
All money raised by the sale goes to the RCA Fine Art Student Award Fund, which helps support emerging artists during their time at the college.
Since 1994, sales of postcards have raised more than half a million pounds for the fund.
Last year more than 800 artists and designers donated more than 1,000 postcards.
The RCA Secret exhibition opens from 21 November and the sale begins on 29 November.