"Today, Islam is faced with the idea that men and women should be equal.
"There are differences between men and women, physically and mentally, so it would be a stupid idea to suggest that all women do what men do and all men do what women do," he told the audience at the International Islamic Forum here on Friday.
Dr Mahathir said Muslims should be prepared to defend their stand that there is no such thing as absolute equality between the sexes.
Dr Mahathir had said on Thursday that there was no law to prohibit a woman from becoming PM.
He also said that Malaysian men were becoming lazy as more women had successfully entered institutions of higher learning and earned higher salaries than their male counterparts.
This had led to many women being forced to marry men with lesser qualifications than them, he was quoted as saying.