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By virtue of combining an in-situ assembly process with a stepwise synthesis in conventional aqueous solution, two series of unique organic-inorganic hybrid heteropolyoxomolybdates were constructed from plenary Keggin germanomolybdates and Cu-Ln heterometallic units and fully characterized: [H 2 INA] 2 H 8 [LnCu(INA) 4 (H 2 O) 6 ] 2 [α-GeMo 12 O 40 ] 3 ⋅52 H 2 O (Ln=La 3+ (1), Ce 3+ (2), Pr 3+ (3), Nd 3+ (4), Sm 3+ (5), Eu 3+ (6); HINA=isonicotinic acid) and (NH 4 )[Cu(PA) 2 ][Cu(PA) 2 Ln(H 2 O) 8 ][α-GeMo 12 O 40 ]⋅10 H 2 O (Ln=Nd 3+ (7), Sm 3+ (8), Eu 3+ (9); HPA=picolinic acid). The most remarkable structural characteristic of compounds 1-6 was that their molecular units were defined by three discrete plenary Keggin [α-GeMo 12 O 40 ] 4- polyoxoanions and two organic-inorganic hybrid heterometallic [LnCu(INA) 4 (H 2 O) 6 ] + moieties, whereas compounds 7-9 exhibited a nice-looking 1D chain-like structure that was built from plenary [α-GeMo 12 O 40 ] 4- polyoxoanions, pendent [Cu(PA) 2 ] complexes, and bridging {[Cu(PA) 2 ][Ln(H 2 O) 8 ]} 3+ heterometallic groups. Notably, two different pyridine carboxylic acid ligands led to the discrepancy between the two structure types. To the best of our knowledge, compounds 1-9 constitute the first examples of plenary Keggin heterometallic germanomolybdates that include Cu-Ln-organic subunits. Further studies revealed that compounds 3 and 8 exhibited fast adsorption capacity for cationic dyes methylene blue (MB) and rhodamine B (RhB) in water. Moreover, compounds 3 and 8 could quickly and selectively adsorb MB from a mixture of MB/methyl orange (MO) or MB/azophloxine (Apo)., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)