Abstract: Sulfonylcarbanion can be converted into alkene by elimination⁽¹⁾(eq 1),mix-coupling⁽²⁾ (eq 2) or homocoupling⁽³⁾ (eq 3) under iron catalysis. Besides desired alkenes, isomerized alkenes were detected in the reaction of elimination or mix-coupling. However, no migration of double bond in alkene was found in homocoupling reaction. Some experimental results were obtained to discuss the alkene isomerism in the iron-catalyzed sulfonylcarbanion olefination and some evidences were given to support the proposed mechanism of iron-catalyzed sulfonylcarbanion olefination.