Previous investigations on the effects of temperature and impurities on the, surface tension of molten silicon, and relevant measurement methods have been reviewed, and the influence of oxygen partial pressure (P-O2) in the atmosphere has been analyzed emphatically, on the basis of the results obtained by the sessile drop method and calculations. In the case of P-O2 less than or equal to P-O2.(sat) (the saturated oxygen partial pressure in the Si(l)-O-2(g)-SiO2(S) system), the surface tension First remains almost constant and then decreases remarkably with the increase of P-O2, the temperature coefficient of surface tension (partial derivativesigma/partial derivativeT) is negative and increases with the oxygen partial pressure, and the molten silicon drop is very sensitive to outside vibrations, However. in the case of P-O2 > P-O2.(sat) the surface tension increases slightly with the oxygen partial pressure, partial derivativesigma/partial derivativeT is higher and also increases with P-O2 the molten silicon drop is not influenced by environmental disturbances and remains stable, and EPMA (electron probe microanalyzer) analysis indicates the formation of a thin SiO2(S) film on the surface of the molten silicon drop which might account fur the surface tension increase.