AbstractThe heterogeneous phase transition of the organic vapours, cyclohexane and p‐xylene, on a cold substrate was observed by cooling the substrate at a slow rate under reduced pressure conditions. Either organic vapour at a vapour pressure lower than 130 Pa formed directly solid crystals but p‐xylene vapour at a higher vapour pressure formed liquid condensates with subsequent formation of solid crystals. The dependence of the critical supersaturation ratios on the critical temperatures and the physical properties of the organic vapours has been clarified by the equation derived on the basis of classical nucleation the