The effects of different assist gases, O-2, Ar, N-2 and compressed air. during laser percussion drilling are investigated with regard to the physical features, i.e., thickness and surface geometry, of the resulting spatter and its bonding strength. Laser drilling was conducted on NIMONIC 263 alloy sheets, 2.6 mm thick, using a fibre-optic delivered 400-W Nd:YAG laser. The work has revealed that the spatter generated with O-2 assist gas is distinctly different from those produced with N-2, Ar and compressed air. Thr influence of the assist gas type on the mechanism of material ejection/removal is reported. The spatter bonding strength has been found to be associated with the 'inertness' of the assist gas employed, in which a progressive increase was observed in the order of O-2, compressed air, and N-2 and Ar. It appears that the spatter bonding strength is dependent on the assist gas type and the workpiece material composition. In addition, it was found that the overlapping of spatter between adjacent holes. in closely spaced array holes, possessed higher bonding strengths. Consequently, the removal of overlapped spatter produced with inert assist gases is difficult to achieve without causing undesired modification to the material surface and hole geometry.