Studies of the use of agricultural wastes or natural resources as cement replacements have increased in recent years. The evaluation of their pozzolanic activity is essential to predict the behavior of modified cementitious materials elaborated with these resources. This work presents a study of the pozzolanic activity of bamboo stem ashes, which were obtained by calcining bamboo stem at 600 °C for 3 h in a calcination furnace. Several methods such as Chapelle test, saturated lime method, thermogravimetric analysis and strength activity index were proposed to evaluate the pozzolanic activity. The results of X-ray fluorescence and X-ray diffraction indicate that bamboo stem ashes are mainly composed of Silica (SiO2) with an amorphous phase. The Chapelle test and the saturated lime method showed the pozzolanic activity of bamboo stem ashes. Finally, at 7 and 28 days, mortars containing 10 % by weight of bamboo stem ashes show a strength activity index greater than 75 % as recommended by ASTM C618.