In the present work, a kilojoule plasma focus device, PF-2 kJ, is adopted as a pulsed x-ray source to study the effects of pulsed radiation in cancer cells. Low dose hyper-radiosensitivity (LDHRS) effects have been explored in various cancer cell lines using conventional x-ray irradiation. To the best of our knowledge, the LDHRS effects have not yet been explored using pulsed x-rays. Cell death was evaluated in human colorectal (DLD-1 and HCT-116) and breast (MCF-7) cancer cell lines (monolayer cell cultures) irradiated with 10 (∼0.24 Gy), 20 (0.61 Gy), and 40 (∼1.1 Gy) pulses (FWHM ∼90 ns, dose rate ∼107 Gy/min with a dose of 0.025 Gy per pulse). The LDHRS cell death effect in the DLD-1 cell line irradiated with pulsed x-ray is three times higher than the reported for a conventional continuous x-ray source at two times higher doses. LDHRS was also observed in HCT-116 and MCF-7 cells exposed to 10 and 20 x-ray pulses, respectively, which are reported not to exhibit LDHRS when conventional continuous x-ray sources are used. Besides, a normal colorectal cell line, CCD-841-CoN, does not show a significant cell death at 10 pulses. These preliminary results suggest a selective effect of low-dose pulsed x-rays on cancer cells. The present work demonstrates the applicability of plasma focus devices for cancer research. Further possibilities in the exploration of pulsed x ray of high-dose rate and low total dose in radiotherapy research are opened.