Flow and temperature fields of natural convection in a hemisphere were visualized by using thermo-sensitive liquid crystal powder. Water, aqueous glycerin and silicon oils were used as working fluids in the experiment. The ranges of Rayleigh and Prandtl numbers based on the fluid bulk temperature and radius of the hemisphere were 1×10 5<Ra<1.4×10 9 and 6<Pr<10000, respectively. The results indicated that fluid flow in a hemisphere could be classified into three flow patterns. Steady circulating flow, i.e., fluid rose up at the center of the hot surface and descended along the hemispherical inner surface, was observed at about Ra=1.9×10 5. For Ra>2×10 5, thermal boundary layer separated from the hot surface and hot thermal plumes were released periodically. The regular separation was maintained up to about Ra=4×10 7-10 8. For Ra>10 8, however, observation of flow showed that the release of hot thermal plumes became irregular and finally the transition of flow from laminar to turbulent might be completed in this Rayleigh number range.