Perpetrators film or photograph women with hidden cameras in public spaces.
Although distributing pornography is illegal in South Korea, the videos and pictures are shared widely online.
Organisers say women live in constant fear of being photographed or filmed without their knowledge.
Carrying placards and banners with messages like "My life is not your porn", the women were mostly teenagers or in their 20s - seen as the main victims of the hidden cameras.
"Those men who film such videos! Those who upload them! Those who watch them! All of them should be punished sternly!" they chanted.