Abstract: Although the problem of effective utilization of coal powder fl y ash(CPFA) has given rise to wide attention for last twenty years， ye t only less than half of useful CPFA in China is presently utilized. Alte rnat ive way to the problem of CPFA disposal would be to make use of mineral matter i n the ash. Under the existing economic conditions， one of the resource compone nts of coal ash which may be considered for their intrinsic value is the glass m icro spheroids (including cenospheres). The physical and microstructural characteris tics of the glass microspheroids in CPFA from the Huaneng Nanjing Electic Power Plant， such as shape， particle-size distribution， types of particles， chemi cal compositions， species and contents of mineral phases， weight percentage of cenospheres ， density and crustal thickness of microspheroids， as well as their thermal st ability etc.， were studied by the modern analytical techniques in detail and t he formation mechanism of cenospheres were discussed in this paper. 　　Cenospheres make up only less than 0.5% of the CPFA from the Nanjing Electric P ower Plant. The particle-size distribution of the cenospheres shows that the p articles with diameter less than 80μm are about 14.7%; between 80μm and 150u m, about 58.4%; more than 150μm, about 26.9%. The chemical c omposi tions of cenospheres are similar to CPFA in SiO2 and Al2O3， but higher in CaO and K2O, and lower in Fe2O3 than those of CPFA. The main mineral com po nent of the cenospheres is a glass phase(more than 90%). The crystalline phases include only α-quartz (absence of β-quartz) and mullite. The microspheroids which are sinkable in water have the chemical composition similar to CPFA. Thei r main mineral component is also a galss phase， and the crystalline ph ases are the same as CPFA including α-quartz， β-quartz， mullite， magnetit e and hematite etc. 　　The formation mechanism of glass microspheroids (including cenospheres) is close ly related to the petrographic composition and microstructure of coal, as well a s its combust ion in different conditions. The tests of coal combustion at high temperatures show that the coal containing more volatiles is favourable for formation o f cenospheres. The micropores in coal have much a greater effect on the format ion of glass microspheroids than the submicropores.Much work remains to be done in this area.