Acetals and ketals are among the most important perfume materials and industrial materials of organic synthesis. Up to now, there are many methods to synthesize them.Conventionally H2SO4 is used as catalyst in factories, but it causes many problems, such as the erosion of equipment, difficulty for after-treatment, low quality of the products, etc. Heteropolyacids (HPA) and their salts have been extensively studied because of their interesting catalytic properties.Significant research effort has been directed towards the entrapment of heteropolyanions in suitable polymeric matrices with the main goal of preparing a new type of polymer-supported catalyst for various applications in heterogeneous and electrocatalysis. It showed that the main catalysis of HPA occurs through Brφnsted acid. The reports pointed that the rate of dehydration and etherification is directly in proportion to total acidity of heteropolyacids, HPA and its salts showed excellent catalytic activity to the esterification and have recently attracted much attention as catalysts for various industrial processes, because that their acidic and redox properties can be controlled at atomic/molecular levels. Mizuno and Misono, Pope, Kozhevnikov and Wang Enbo have reviewed the homogeneous catalysis and fine organic synthesis catalyzed by heteropoly compounds.Polyaniline (PAn) is another example of a polymer host which can accommodate anions originating from 12-tungstophosphoric acid (PW12). The polyemeraldine base was prepared by condensation-polymerization of aniline in aqueous HCl using (NH4)2S2O8 as the oxidant.PW12/PAn can be achieved by doping the protonation of the polyemeraldine base with H3PW12O40 in a two-step procedure. However, there is no report on the synthesis of 2-methyl-2-ethyl acetoacetate-1,3-dioxolane catalyzed by PW12/PAn.In this paper, 2-methyl-2-ethyl acetoacetate-1,3-dioxolane was synthesis from ethyl acetoacetate and ethylene glycol in the presence of PW12/PAn. The factors influencing the synthesis were discussed and the best conditions were found out. The optimum conditions are: molar ratio of ethyl acetoacetate to ethylene glycol was 1:1.5, the quantity of catalyst was equal to 1.0% of feed stocks,and the reaction time was 50 min. PW12/PAn was an excellent catalyst for synthetizing 2-methyl-2-ethyl acetoacetate-1,3-dioxolane and its yield can reach over 81.0%. IR spectra of 2-methyl-2-ethyl acetoacetate-1,3-dioxolane shows peaks at 1738,1375,1244,1188,1047 cm-1;1HNMR (δH, ppm): 4.16 (q, 2H, CH2), 3.98 (s, 4H, OCH2CH2O), 2.62 (s, 2H, CH2), 1.46 (s, 3H,CH3), 1.22 (t, 3H, CH3); nD20=1.4320; b.p. 126-128 ℃/6.7 kPa.