Aerosol-induced laser breakdown thresholds has been discussed in different optic parameter or in different micro-meter sized particles using a mode-locked Nd:YAG laser with 123.61ps pulse duration irradiates aerosol particles (Al2O3、ZnO、ZrO2、18th glass) that are suspended in air. Following results are obtained:breakdown thresholds for aerosol particles (d >30m m) are 2~3 order of magnitude below those for clean air (d >1m m). Air breakdown threshold is lower as laser radius increasing or aerosol particle size increasing. The threshold depends on particles composition The threshold is higher as laser wavelength decreasing.