Previous strap lines included 'Stars eat Mars'
After 40 years Mars is replacing the slogan with "Pleasure you can't measure".
Slough-based Mars said the "more contemporary" look of the new bar would appeal to both men and women alike.
"The images of energy and accomplishment have a male bias," said a spokeswoman.
"Mars bars are eaten by equal numbers of men and women, but in the market generally, more women eat chocolate than men.
"So we are trying to redress the balance and make it more appealing to women."
Weight loss
Since the first Mars bar was handmade in Slough in 1932, it has had several strap lines - such as "Stars eat Mars".
BBC consumer affairs correspondent Nicola Carslaw says the new look packaging will still be gold, black and red.
But although the 29p price for a standard size bar will stay the same, the new standard size will actually be 2.5grammes smaller, leaving consumers a tiny bite short.
The recipe for the bars will remain the same but the nougat filling will be whipped more "to increase the feeling of lightness", Mars said.
Mars has launched the new look to boost flagging sales of the bar, which reportedly dropped from 2 billion to 1.09 billion last year.