Geopolymer–zeolite hybrid bulk materials were formed in-situ from as-received coal fly ash powder by a simple two-step treatment: (1) immersing the coal fly ash powder packed within a cylindrical acrylic pipe into a 3.5 mol/l Na(OH) solution at 80°C and (2) subsequent curing in a temperature–humidity-controlled chamber at a fixed condition: 50°C and 50% relative humidity. The content of the formed Na-X type (conversion ratio from the starting coal fly ash) in the sample was optimized to be approximately 10% when the duration of the immersion in Na(OH) solution reached 72 hours. The compressive strength at room temperature of the in-situ formed bulk samples exhibited a clear tendency to increase with both alkali immersion time and curing time, which could be due to the increase of the amount of the in-situ formed geopolymer. As a result, after the 96-hour-alkaline immersion followed by the 21 days curing, the average compressive strength at room temperature achieved 5.4 MPa. This value was found to be more than four times higher than that of the samples without curing treatment (1.3 MPa).