Two new multi-cobalt-containing polyoxotungstates K 4 Na 6 Co 2 (H 2 O) 12 {Co(H 2 O) 4 [Co 2 (H 2 O) 10 Co 4 (H 2 O) 2 (B-α-SiW 9 O 34 ) 2 ] 2 }·40H 2 O (1) and K 10 Na 2 [Co 4 (H 2 O) 2 (GeW 9 O 34 ) 2 ]·20H 2 O (2) have been obtained by the routine synthetic reactions in aqueous solution. The polyoxoanion framework of 1 consists of two sandwich-type polyoxoanions [Co 4 (H 2 O) 2 (B-α-SiW 9 O 34 ) 2 ] 12− connected together by a [CoO 2 (H 2 O) 4 ] cluster to constitute the sandwich dimer, and then, four isolated Co(H 2 O) 5 cations coordinate to the dimer through four μ 2 -O atoms. The polyoxoanion 2 is isomorphic to the sandwich-type polyoxoanion [Co 4 (H 2 O) 2 (B-α-SiW 9 O 34 ) 2 ] 12− in 1. The magnetic property of compound 1 has been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0K, indicating the existence of intramolecular ferromagnetic Co–Co interactions, and, the electrochemical properties of 1 and 2 are detected in the pH 4 buffer solution.