The unique thermoresponsive phase behaviors of diblock copolymers from amino acid-derived vinyl monomers have been demonstrated in view of variation in the aggregation state in water. Amino acid based block copolymers composed of N-acryloyl-Ala-methylester (NAAMe) and N-acryloyl-beta Ala-methylester (NA beta AMe) are successfully synthesized by RAFT polymerization. The resultant block copolymers poly(NAAMe(48)-b-NA beta AMe(m)) contain a constant degree of polymerization (DP= 48) of the poly (NAAMe) block, but the DP of the poly(NA beta AMe) block varies (m = 80-122). The turbidimetry subjected to these copolymer aqueous solutions exhibits two LCST transitions upon heating. In the 1st LCST region, the block copolymer forms a relatively loose-molecular packing, while large aggregates due to partial dehydration of polymer molecules, which subsequently transform into a stable micelle structure in a region of 30-39 degrees C. Finally, a tight aggregate composed of the dehydrated micelles is formed. Temperature-dependent H-1 NMR spectroscopy of the diblock copolymers also supports such a postulation for the dual phase transitions and stable micelle structure formation. In addition, a typical salting-out effect is observed in the thermal behavior of the polymer, but a serious cytotoxic effect is not observed in NIH beta T3 cells, suggesting that the novel diblock copolymers are relevant for biomedical applications. (C) 2017 Elsevier Inc. All rights reserved.