Two biogenetic guanidine carboxylates, i.e., creatinine acetate (CRA) and creatinine glycolate (CRG) based on creatinine (CR) were synthesized and structurally characterized by (1)H NMR, (13)C NMR and X-ray diffraction (XRD) analysis of the single crystals. The characterization demonstrated that CRA and CRG are CR-guanidinium carboxylates in nature, and the carboxylates are associated with the guanidinium via hydrogen bonds. CRA and CRG were successfully used as single-component initiators for ring-opening polymerizations (ROPs) of l-lactide (LLA), dl-lactide (DLLA) producing polymers with controlled molecular weights and narrow polydispersities (PDI = 1.16-1.26). The investigation on the kinetics of the ROPs indicated the typical characteristics of living polymerization as evidenced by the linear relationship of ln [M](0)/[M](t) versus time and M(n) (number-average molecular weight of formed polymer) versus monomer conversion. A study of the terminator-adding effect on the growing polymers revealed that the polymerization follows the coordination propagation mode. The structures of the living oligomers and product polymers were characterized with (1)H NMR spectroscopy. The mechanism of the polymerization was proposed on the basis of the experimental investigation.