The composition for hard tissue repair of the present invention is characterized by comprising 5 to 98.95 parts by weight of a monomer (A), 1 to 75 parts by weight of a (meth) acrylate polymer (B) and 0.05 to 20 parts by weight of a polymerization initiator composition (C) containing an organoboron compound (c1), with the proviso that the total amount of the components (A), (B) and (C) is 100 parts by weight. The composition undergoes small-scale heat generation during curing and can ensure a sufficient working time.本發明的硬組織修補用組成物係包含單體(A)5~98.95重量分、(甲基)丙烯酸酯聚合物(B)1~75重量分、以及含有有機硼化合物(c1)的聚合起始劑組成物(C)0.05~20重量分((A)、(B)、以及(C)之總和為100重量分)。該組成物硬化時的發熱少，而且可確保充分的作業時間。
