At many stock exchanges of world, it is applied from price limit for different purposes including: reducing frequency and manipulation of stock. One of the most important effects of price limit is magnet effect that is available in most of stock exchanges of world. The magnet effect on Tehran stock exchange is proved and in this article we decide to study this effect on Tehran stock exchange and role of active investors at stock market. Studies on 24 companies as case study including: Kesaveh, Ghalrest, Shomal Excavation, Betras, Khazamia, Khasapa, Sefars, Sina, Fazer, Fasmin, Ghapira, Ghanisha, Kermasha, Koravi, Vitro, Sapa, Sakht, Sepah, Sandogh, Lesapa, Melat and Madan reveal that except one case (Gheshkar) in all of the companies the role of institutional investors on magnet effect is higher than non-institutional investors.