<p>In this study, additive-free coal fly ash was sintered to prepare glass-ceramics. Research revealed that residual carbon and sulfur in CFA adversely affect the densification degree of glass-ceramic. Following the initial decarburization process, the sintered glass-ceramics exhibited a notable rise in linear shrinkage. When it comes to ultralow basicity CFA, the sintering performance was significantly influenced by the particle size of the raw material. When sintered at 1150&#xa0;°C, the raw material with a <i>D</i>_<i>v</i>(50) of 7.55&#xa0;<i>μ</i>m exhibited a shrinkage rate of only 5.07 pct, whereas the raw material with a <i>D</i>_<i>v</i>(50) of 0.651&#xa0;<i>μ</i>m achieved a shrinkage rate of 21.45 pct. Additionally, increasing the sintering temperature facilitated the improvement of the glass-ceramic’s density, however, too high temperature impaired the shrinkage due to the generation of sulfur-containing gases. Furthermore, a comparison of the effects of CFA compositions on sintering and crystallization revealed that CaO significantly lowered the sintering temperature and promoted the densification process. When the CaO content was low, the predominant crystalline phases were mullite and cristobalite. Using raw material with a <i>D</i>_<i>v</i>(50) of 1.06&#xa0;<i>μ</i>m and sintering at 1150&#xa0;°C for 1&#xa0;hour, the glass-ceramic demonstrated a flexural strength of 172.2&#xa0;MPa. Additionally, it exhibited excellent resistance to both acid and alkali, with values reaching 99.97 and 99.31 pct, respectively. Therefore, utilizing CFA to prepare additive-free glass-ceramics is a feasible and promising method that enables efficient utilization of CFA.</p> Graphical Abstract <p></p>