[en] Experimental properties of monster sawtooth activities in ohmic HT-7 plasma are presented. The monster sawtooth activities belong to global fluctuations and are characterized with a series of large core collapses on SXR intensity traces with a long period, a large amplitude fluctuation and a large inversion radius, However, they emerge without apparent deterioration of plasma confinement and without major plasma disruption. During the events, long partial sawtooth collapses and abundant MHD phenomena are also observed