The present experiment applied the freeze cracking technique and scanning electron microscopy for further studies of ultrastructural changes of cancer cells after they invaded into the organ. It was found that, after two days of cultivation, there were a lot of cancer ceils which adhered on to the surface of organ fragments. The cancer cells migrated on the surface of the organ and at the same time penetrated into the organ by stretching out their pseudopodia. After 3 days of cultivation, some cancer cells had already invaded into the organ. After invasion they connected target cells of the organ by different ways, but their filopodium is the important organelle for the connection and communication with those target cells.The cancer cells caught the projecting portion of surface of target cells by branches of filopodia forming a mosaic pattern with them. Sometimes the filopodia of cancer cells fused with the opposed surface of target cells by inserting into it. Some filopodia became short and thick inside the organ due probably to the limited distance between cancer cells and target cells when they were in close contact to each other. Once the tumor cell nests were formed in the organ, the tumor cells connected each other by stretching out pseudopodia from both poles, but kept a definite space between cells. It is postulated that these inter-cellular spaces were formed probably by the repelling force of the identical electric charge of the tumor cell membranes.