Aggregates formed from amphiphilic alternating copolymer samples of sodium maleate and dodecyl vinyl ether (MAL/C12) of different molecular weights or (weight-average) degrees of polymerization N-w1 (= 76-5000) were characterized by light scattering and fluorescence techniques in 0.05 M aqueous NaCl at pH 10 to investigate the molecular weight dependence of the micellar structure of amphiphilic polyelectrolytes. The light scattering and fluorescence data demonstrated a unicore-multicore transition of the MAL/C12 micelle at N-w1 approximate to 300. The structures of unicore and multicore micelles of MAL/C12 copolymers formed were analyzed using the flower micelle model and the flower necklace model, respectively. The data points for unicore: micelles formed from the three low-molecular-weight MAL/C12 fractions were in good agreement with the flower micelle model of the minimum loop size determined by the rigidity of the polymer main chain, which we proposed previously [Kawata et al. Macromolecules 2007, 40, 1174-1180]. On the other hand, the data points for the four high-molecular-weight MAL/C12 fractions were nicely fitted to the flower necklace model, the conformation of which was represented as the touched bead model.