AbstractThe surface roughness in plane milled Scots pine wood that was thermally modified at 190 °C and 220 °C was examined. Indicators of wood surface roughness included the three most commonly applied parameters, arithmetic mean surface roughness (Ra), surface roughness depth (Rz), and total height of the roughness profile (Rt). Roughness was tested separately for earlywood and latewood using two feed speeds of 1 and 5 m/min. The thickness of the milled layer was 1 mm. The effect of all controlled factors, i.e., feed speed, temperature of modification, and place of measurements, on the parameters of surface roughness were statistically significant (P < 0.05). Surface roughness increased with an increase in feed speed, whereas it decreased with an increased modification temperature. Latewood was characteristically lower in roughness than earlywood. The greatest differences in homogenous groups for the determination of the roughness parameters were found in measurements taken on earlywood and latewood, while the smallest differences were recorded for different feed speeds.