Activated carbon (AC) was successfully prepared from low-cost forestry fir bark (FB) waste using KOH activation method. Morphology and texture properties of ACFB was studied by scanning and high-resolution transmission electron microscopies (SEM and HRTEM), respectively. The resulting of fir bark based activated carbon (ACFB) demonstrated high surface area (1552 m2/g) and pore volume (0.84 cm3/g), both of which reflect excellent potential adsorption properties of ACFB towards methylene blue (MB). The effect of various factors, such as pH, initial concentration, adsorbent content as well as adsorption duration were studied individually. Adsorption isotherms of MB were fitted using all three non-linear models (Freundlich, Langmuir and Tempkin). The best fitting of MB adsorption results was obtained using Freundlich and Temkin. Experimental results showed that kinetics of MB adsorption by our ACFB adsorbent followed pseudo-second order model. Maximum adsorption capacity obtained was 330 mg/g, which indicated that fir bark is an excellent raw material for low-cost production of activated carbon suitable for cationic dye removal.