Many studies on cancer therapy apply conduct of apoptosis by pulse electric fields have been actively started. In this study, in vivo experiment of applying nanosecond pulse electric fields (nsPEFs) on solid tumors are carried out. To advance this study, we adopt the embryonated chick assay, which can easily prepare a large number of samples for test, compared to typical animal experiments. The tumor cells: EMT6/KU (mouse breast adenocarcinoma cells), were planted with capillary on chorioallantoic membrane in fertilized chicken egg. After four days from this process, nsPEFs of 2ns pulse-width were applied on the solid tumor. The tumors were dissected from eggs after three days from the nsPEFs application and were weighed. The control eggs without nsPEFs application were also processed with the same procedure. Difference of the weights of the pulse-treated and controls tumors was confirmed to be significant by using statistics processing. The weights of the tumors decreased with increase of charging voltage of generator. Tumors treated with nsPEFs exhibited apoptosis by TUNEL staining.