The thermal, mechanical, and morphological properties of biobased thermoplastic starch (TPS) obtained from agricultural waste seed (AWS) and agricultural waste tuber (AWT) blended with polypropylene (PP) were investigated in this article. The grounded (pulverized) AWS and AWT were different in amylose/amylopectin ratios and contained relatively low starch content (<= 50%). The commercial grade of TPS (CS) and native tapioca starch blended PP (NTS/PP) were also prepared for comparison. The performances of the TPS/PP blends were dependent on the starch composition (e.g., amylose-to-amylopectin ratio), particle size, dispersion, and interfacial adhesion with matrix. The high-amylopectin starch blend (i.e., AWS/PP) was more susceptible to thermal degradation than the amylose-rich material (i.e., NTS/PP). The addition of starch to PP not only led to a stiffening effect (i.e., increase in storage modulus), but it also affected the relaxation of polymer matrix by shifting the thermal transition (i.e., glass transition temperature) to a higher temperature. POLYM. ENG. SCI., 54:1357-1365, 2014. (c) 2013 Society of Plastics Engineers