The reduction of selenious acid solution with hydrazine hydrate in the presence of poly(vinylpyrrolidone) (PVP) can produce a stable dispersion of uniform and amorphous selenium particles capped with PVP with a size of 100 nm. Further addition of a solvent with low polarity such as n-butyl alcohol into this aqueous solution and mild stirring result in the transportation of amorphous selenium particles onto a liquid-liquid interface between water and n-butyl alcohol. Subsequent crystallization and shape evolution on this interface occurred and finally resulted in the formation of singe crystalline selenium nanorods. The results demonstrated that the enrichment of nanoparticles with amphiphilic property at a liquid-liquid interface between a polar solvent and another solvent of low polarity can result in crystallization and phase transformation for the formation of nanostructures.