Construction and performance of a low‐cost easy‐to‐build CO2laser beam profile monitor are described. Its specifications correspond to those of commercial devices. In this monitor a small slit covered by a temperature dependent fluorescent surface is imaged on a photodiode. A rotating mirror scans the spatial intensity distribution over the slit. This allows one to avoid an expensive photodiode array. The signal‐to‐noise ratio is improved by repetitive sampling with a low‐cost digital processing unit. The dynamic range of measurement is 7 to 1 and the linearity is 10% within this range.