Min, C.-K. Eom, I. Hu, J. Jung, S.H. Kang, H.-S. Kim, S.H. Lee, H.-S. Park, S.S. Toward 10 fs Timing Stability of PAL-XFEL JACoW Publishing Geneva, Switzerland PAL-XFEL demonstrates 20 fs jitter in e-bunch arrival time at the end of undulators and its pump-probe system, which is extremely useful for maintaining high stability of machine and time-resolved experiments with high time resolution. Our low phase noise timing system and high stability high power RF system enable this low jitter. Our measurement shows 10 fs jitter of e-bunch arrival time at the injector and it increased ~20 fs due to e-bunch energy variation. The possibility of improving the final jitter is described based on the optimization of bunch compressors and longitudinal feedback.