In the condensation of arylaldehydes with arylethylidenemalononitriles, it was found that, besides the normal product dienes a, the ring-closure product quinoline derivatives b can be also obtained in 26%—50% yields. The substituent effects were also examined and a possible reaction mechanism was proposed for the formation of b. The X-ray crystal structure of 1b confirms the structure of the ring-closure product. In the condensation of arylaldehydes with arylethylidenemalononitriles, it was found that, besides the normal product dienes a, the ring-closure product quinoline derivatives b can be also obtained in 26% -50% yields. The substituent effects were also examined and a possible reaction mechanism was proposed for the formation of b. The X-ray crystal structure of 1b confirms the structure of the ring-closure product.