Well-defined amphiphilic poly(β-malic acid-b-ε-caprolactone) diblock copolymers with tunable hydrophobic content have been synthesized. For the sake of comparison, amphiphilic α-lauryl, ω-methyl poly(β-malic acid) has been synthesized as well. The stability of the block copolymers in aqueous solutions against hydrolysis has been demonstrated, at least within a period of time long enough to rely on tensioactive measurements by the pendant drop method. The critical micellar concentration of such amphiphilic (co)polymers has been determined by dynamic light scattering. The effect of pH, temperature, salt (NaCl) addition, and copolymer composition has been investigated. Whatever the copolymer composition, it has been shown that increasing pH from 2.2 to 8.5 increases surface tension in water. In contrast, reducing the length of the hydrophobic block lowers the surface tension in water but also the mean diameter of micellar structures.