Tetraalkyltelluriums (R4Te) react with arylacetylenes (ArCCH; Ar = Ph, p-MeOC6H4, p-FCeH4) to afford alkylation products (ArHCCHR). The alkylation proceeds preferentially in net trans fashion to give a cis-1,2-disubstituted olefin as the major product along with the concomitant formation of a tellur ide (R2Te) and an alkene originated from a substituent of R4Te which plays as a hydrogen source. The reaction of dibutyldidecyltellurium (nBu2TenDec2) with phenylacetylene yields nearly statistical ratios of products, PhCHCHnBu (41%, E/Z = 10/90), PhCHCHnDec (35%, E/Z = 11/89), nBu2Te (20%), nBuTenDec (41%), and nDec2Te (18%), indicating a random transfer of primary alkyl substituents. On the contrary, nBu2TeiPr2 reacts with phenylacetylene much faster than nBu4Te affording only PhCHCHiPr. Under similar conditions Ph4Te does not react with phenylacetylene and nDec2TePh2 decomposes quickly to nDecTePh (95%), 1-decene (93%), and benzene (99%). The alkylation is proposed to proceed by the radical addition of R4Te to ArCCH to yield (R3Te) ArCCHR, which then decomposes to afford an olefin via a β-hydrogen transfer from R on tellurium to the vinyl carbon.