Recently, the development of materials for reducing the environmental problems is an important issue. Bio-based materials from renewable resource gain lot of interests because they can be alternatives to petroleum-based materials. So to reduce the environmental impact from waste, bio-based materials should be used to produce thermoplastic elastomer materials. In this study, polylactide and natural rubber latex (NRL) were chosen as raw materials for a new thermoplastic elastomer via admicellar polymerization. Admicellar polymerization is the technique to coat polymer thin film onto the substrate surface by bilayer of surfactant which acts as a reaction template for polymerization. By using constant concentration of NRL substrate of 0.05 g/ml, the lactide monomer content (200, 500, 800, and 1000 mM) was varied to find the suitable concentration of lactide monomer for bio-thermoplastic elastomer applications. Fourier transform infrared spectra of the admicellar synthesized natural rubbers showed the characteristic peak of polylactide. The core-shell structure of polylactide coated onto natural rubber latex particles was revealed by transmission electron microscope (TEM). The bio-thermoplastic elastomers were characterized by dynamic mechanical analysis (DMA) for the glass transition temperature (Tg), behavior of materials and by melt flow index testers for measuring of the ease of flow of the molten bio-thermoplastic elastomers .