Abstract In industry, rapid crystallization is often required. At present, the crystallization rate of poly(lactic acid) (PLA) is too low compared to industrial needs. In this paper, amino acids such as glycine and L-alanine and poly(amino acids) like polyglycine and poly-DL-alanine are considered as heterogeneous crystallization nucleating agents. The impact of adding these bio-based additives on the isothermal crystallization behavior of PLA was quantified and compared at different concentrations by using the so-called Lotz efficiency scale, which here is based on isothermal DSC measurements. In addition, rheological and rheo-optical techniques were used to monitor the isothermal crystallization. Our results indicate that polyglycine possesses a significant nucleating ability (60.5%) which is comparable to the industrially used talc (81.1%).