Ding, Y. TUA01 2015 2015-12 Generation of high power, femtosecond to sub-femtosecond X-ray pulses is attracting much attention within the X-ray free-electron laser (FEL) user community. At the existing FEL facilities, such as the Linac Coherent Light Source at SLAC, low-charge operation mode and emittance-spoiling foil scheme have been developed to deliver sub-10 fs X-rays to user experiments. We recently performed extensive measurements on these two modes using the X-band transverse deflector diagnostic at LCLS, demonstrating a flexible pulse duration control with direct measurements. To achieve sub-fs X-ray pulses, a simple nonlinear compression mode has been recently developed with pulse duration about 200 as [1]. Experimental study of this sub-fs mode will be pursued in this year. We report the recent experimental studies for generating femtosecond to sub-fs x-ray pulses.