Disclosed are a polysilsesquioxane having a ladder structure with photoactive groups bonded at the siloxane main chain, and a method for preparing the same. Polysilsesquioxanes exhibiting superior thermal and mechanical properties and having various functionalities and characteristics depending on the photoactive groups introduced thereto may be prepared via a relatively simple method. The polysilsesquioxanes may be useful as an industrial material for organic-inorganic hybrid materials.