High‐temperature bamboo‐char is a potential polymer reinforcement due to its porous structure, high strength and modulus. To improve the surface structure and properties of bamboo‐char, different concentrations of HNO3 and NaOH solution modifications were conducted. The HNO3 treatment grafted amino groups on bamboo‐char and NaOH treatment modified carbonyl and carboxyl groups. The specific surface area and the total pore volume of bamboo‐char reduced with HNO3 treatment, whereas the two values firstly increased and then decreased in the case of NaOH treatment; the maximum values of 30.422 m2·g−1 and 0.066 cm3·g−1 were reached at 10 wt% NaOH concentration. The maximum tensile strength and modulus of PLA/bamboo‐char composites were achieved up to 65.36 and 1012.0 MPa at 15 wt% NaOH concentration. The maximum elongation at break was reached at 15.36% and impact strength of 25.69 KJ·m−2 were obtained at the HNO3 concentration of 39 and 54 wt%, respectively. These results will help to extend the application of bamboo‐char in polymer composites. POLYM. COMPOS., 39:E633–E639, 2018. © 2018 Society of Plastics Engineers