In an easily attainable high vacuum (∼ 2×10 −7 torr), the effective work function (φ +) for producing Li + ions from Li atoms impinging upon a polycrystalline rhenium surface was measured as a function of surface temperature ( T ⋍ 1000–2100 K). The data thus obtained show that φ + at T≳1250 K is nearly constant at about 5.5 eV, as if the surface were maintained essentially clean even at T<1750 K, irrespective of adsorption of Li atoms and residual gas molecules (RGM) impinging with fluxes of ∼ 7×10 13−5×10 14 atoms cm −2 s −1 and ∼ 7×10 13 molecules cm −2 s −1, respectively. This is very different from our previous result achieved by impinging LiI molecules with nearly the same flux upon the surface; φ + changes from about 5.5 eV to greater than ∼ 6.4 eV at T ⋍ 1750–1250 K, mainly because of adsorption of RGM. These facts give evidence to support our recent predictions that completely dissociative adsorption of LiI molecules at T≳1250 K has little effect upon φ + because Li and I atoms have opposite effects of decreasing and increasing φ +, respectively, and also that incidence of Li atoms strongly suppresses the work function increase due to adsorption of RGM.