Communication: Complete exfoliation of montmorillonite during Ti-based Ziegler-Natta polymerization of ethylene has been successfully carried out by using montmorillonite (MMT-OH) modified with intercalation agents containing hydroxyl groups. Hydroxyl groups in intercalation agents offer facile reactive sites for anchoring catalysts in between silicate layers. Comparison of exfoliation, characteristics between MMT-OH and non-intercalated montmorillonite showed that the feasibility of exfoliation during ethylene polymerization was highly dependent on the catalyst fixation method.