AbstractThis work aims to design robust and biocompatible nano block‐copolymers (NBCPs) of polycaprolactone@‐polyethylene oxide‐polyaminoacid (PCL@‐PEO‐PAAs) by ring‐opening polymerization. Mechanical behavior including modulus, elongation at yield and break of the tetra block copolymer are studied at room temperature. The significant result lies when the extension at break is reduced by four times with an addition of 2 and 3 wt% of PCL respectively. The tensile strength at yield is found to be 22.39 ± 3.6 MPa, 34.66 ± 5.8 MPa, and 22.906 ± 4.1 MPa for 1, 2, and 3 wt% PCL@‐PEO‐PAAs NBCPs respectively. The partial hydrophobic nature of designed 3 wt% NBCP plays an important role in decreasing the strain at break and increasing the elongation at break of the composites compared to other 1 and 2 wt% NBCPs. In vitro cytotoxicity is observed to be more effective in irregular spheroid shaped 2 wt% compared to 1 and 3 wt% NBCPs due to a greater number of the amphiphilic groups present in the PCL grafted PEO‐PAAs nano BCPs. The ζ potential value for 3, 2, and 1 wt% NBCPs are found to be −26.9, −24.7, and − 15.8 MeV respectively due to higher electrostatic repulsion and became suitably used for in vivo applications.