Abstract: The effect of calcination temperature on the pozzolanic activity of maize straw stem ash (MSSA) was evaluated. The MSSA samples calcined at temperature values of 500, 700, and 850°C were dissolved in portlandite solution for 6 h, thereby obtaining residual samples. The MSSA and MSSA residual samples were analyzed using Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy to determine vibration bonds, minerals, microstructures, and Si 2p transformation behavior. The conductivity, pH value, and loss of conductivity with dissolving time of the MSSA-portlandite mixed solution were also determined. The main oxide composition of MSSA was silica and potassium oxide. The dissolution of the Si⁴⁺ content of MSSA at 500°C was higher than those of the other calcination temperatures. The conductivity and loss of conductivity of MSSA at 700°C were higher than those of the other calcination temperatures at a particular dissolving time due to the higher KCl content in MSSA at 700°C. C–S–H was easily identified in MSSA samples using X-ray powder diffraction, and small cubic and nearly spherical particles of C–S–H were found in the MSSA residual samples. In conclusion, the optimum calcination temperature of MSSA having the best pozzolanic activity is 500°C, but excessive agglomeration must be prevented.