Synthesis of oxindol and 3-oxo-tetrahydroisoquinoline derivatives has attracted much attention of synthetic organic chemists due to their biological activities. On the other hand, we have shown that anodic generation of carbocations at the α-position to the sulfur atom by using an innovative electrolytic system, and these intermediates were successfully trapped by fluoride ions to give various fluorinated compounds. Since anodic oxidation of sulfides has been applied for efficient partial fluorination reactions via the fluoride ion mediated Pummerer type mechanism, we became to be interested in determining whether the electrolytic approach using a fluoride ion mediator might also provide an effective pathway to intramolecular carbon-carbon formation. The starting materials 1 used in this work were prepared from α-phenylthioacetyl chloride and the corresponding amines in THF or CH_2Cl_2 in the presence of Et_3N or K_2CO_3 (Scheme 1). Constant current electrolysis was carried out in acetonitrile containing Et_3N・HF as both a supporting electrolyte and mediator in an undivided cell equipped with platinum plates (2 x 2 cm^2) as an anode and cathode. In the case of electrolysis under ultrasonic irradiation, ultrasonic horn was set vertically 1.5 cm apart from the working electrode (Fig. 1). Electrooxidation of α-(phenylthio)acetamides using a fluoride ion mediator lead to an intramolecular cyclization i.e. C-C bond formation to give the corresponding oxindol and 3-oxo-terahydroisoquindine derivatives. In these cases, a considerable amount of α-fluorinated compounds 3 were formed as by-products, therefore, the yields of cyclic compounds were not satisfactory. However, in the presence of ultrasonic irradiation, the cyclization reactions were accelerated greatly and the desired cyclic compounds 2 were obtained in good yields [Table 1]. The effects of ultrasonic irradiation on the product selectivity and yields were studied in detail [Fig. 2] and the reaction mechanism was proposed. In summary, ultrasonic irradiation can accelerate the fluoride ion mediated anodic cyclization of sulfides to give the desired cyclic products, oxindol and 3-oxo-terahydroisoquindine derivatives in good yields. The local heating effect by ultrasonic irradiation seems to be more advantageous than usual heating. Thus, the electro-synthetic method using ultrasound is considered to be an effective and clean organic synthetic approach.