It is known that π-conjugated polymers can be easily synthesized using monomers which possess metals or halogen atoms as well as transition-metal catalysts. However, in the polymer materials synthesized by such reactions, small amounts of halogens and transition-metal-catalysts remain, often negatively affecting their optoelectronic device performances. Herein, we report a new polycondensation method based on the aldol condensation reaction utilizing the intramolecular resonance effect of the anionic monomer through π-conjugation. We have designed a novel AB type monomer to synthesize the semiconducting poly(oxindolidene thienylene vinylene) (POTV) using the proposed system. Indeed, the polymerization readily proceeded by adding 5-nitro-2-thiophenecarbaldehyde as an initiator after the α-proton abstraction of the oxindole group by the reaction of the monomer precursor with lithium hexamethylsilazide (LiHMDS)/12-crown-4. As a result, the objective POTV with Mn = 3700 and ÐM = 1.47 could be obtained with a good yield (65%). In addition, an organic field effect transistor (OFET) was based on POTV exhibited p-type characteristics, with a hole mobility of 2.24 × 10−4 cm2 V−1 s−1.