Torrefaction of the microalga Chlorella vulgaris was carried out in a fixed-bed tubular reactor under various conditions of temperature (150-300 °C), time (15-60min), and atmosphere (inert or oxidative). The impact of torrefaction and its various conditions on the mass yield, physical properties, chemical composition, and reactivity of the microalgal biomass was assessed and compared with those of the raw material. After torrefaction, the morphology, proximate analysis, ultimate analysis, higher heating value analysis, chemical compositions, and thermal behavior of the biomass were carried out. The results show that torrefaction temperature influenced mass yield and changes in the microalgae’s properties more than torrefaction time and atmosphere. Torrefaction at 200 °C, for 30min in an inert atmosphere led to the highest calorific value of torrefied microalgae. In addition, torrefaction reduced the thermal degradation rates of the remaining protein and carbohydrate fractions in the biomass, but accelerated the degradation rate of the lipids fraction.