Alkali-treatment for modification or dissolution has attracted extensive attention as an innovative means of preparing porous materials. The hierarchical porosity of modified zeolite is highly dependent on its treatment conditions. However, studies on critical alkali-treatment concentrations, specifically those that discuss the dividing points, have not yet been reported. In this article, the pore and crystalline properties of ZSM-5 zeolite samples modified by different concentrations of alkali-treatment are investigated. The experimental results show that the pore properties of the samples change as a function of the alkaline concentration. The total surface, mesopore surface area, total pore volume, mesopore volume, and average pore diameter of ZSM-5 zeolites increase and then decrease with increasing alkaline concentrations. The micropore surface area, micropore volume, and crystallinity of the samples decrease monotonously. The following dividing points are proposed: 0.40 mol/L as the threshold for alkali-modification and 1.00 mol/L as the starting point for alkali-dissolution. A possible desilication mechanism is also proposed.