Laser cutting is a non-contact, non-conventional method for contour cutting which is characterized by several process performances. The present paper aims to analyze the specific cutting energy in CO2 laser cutting of an aluminium alloy using nitrogen as an assist gas. An experimental investigation, based on the use of central composite design, was conducted to define mathematical models for the prediction of the kerf width, surface roughness, and specific cutting energy. Thus, an analysis of the effects of the laser power, cutting speed, and nitrogen pressure on the specific cutting energy is enabled. Moreover, the analysis of experimental data included the correlation between the specific cutting energy and surface roughness. Pareto optimization, considering specific cutting energy and surface roughness, was conducted to propose alternative laser cutting conditions concerning conflicting criteria.