Ultrastrong and transparent bioplastics are generated from fermented microbial monomers. An exotic aromatic amino acid, 4-aminocinnamic acid, was prepared from a bioinass using recombinant bacteria, and quantitatively photodimerized, and diacid and diamino monomers that were both characterized by a rigid alpha-truxillate structure were generated. These two monomers were polycondensed to create the polyamides with a phenylenecyclobutane repeating backbone such as poly{(4,4'-diyl-alpha-truxillic acid dimethyl ester) 4,4'-diacetamido-alpha-truxillamide} which was processed into amorphous fibers and plastic films having high transparency. In spite of noncrystalline structure, mechanical strength of the fiber is 407 MPa at maximum higher than those of other transparent plastics and borosilicate glasses, presumably due to the tentative molecular spring function of the phenylenecyclobutanyl backbone.