We report a new method of preparing patterned nano-crystalline Si (nc-Si) by pulsed laser interference crystallization of a- Si:H thin films. A KrF excimer pulsed laser with wavelength 248 nm and pulse duration 30 ns is employed as a coherent ultra-violet beam source; a one-/two-dimensional (1D/2D) silica phase-shifting grating is used to form a high-contrast laser interference pattern behind it. During the laser treatment, the a-Si:H film is placed behind near contact with the phase grating. A transient thermal 1D/2D grid is then directly formed on the sample, leading to the local crystallization of the a-Si:H films and forming of nano- crystalline Si. The crystallinity of nc-Si films is verified by Raman scattering. Atomic force microscopy clearly shows a morphology of 1D/2D regular sub-micron patterns formed by locally crystallized stripes/dots, which are composed of densely gathered crystallites with a lateral size of approximately 50 - 100 nm and a height of approximately 10 - 20 nm. The interfaces between the crystallized and the amorphous zones are abrupt. Transmission electron micropsy demonstrates a lateral size distribution of nc-Si within the crystallized zones. This new approach has a potential application in the nano-electronics and nano-optoelectronics.