The effects of quenching from the melt on the isothermal crystallization of star-shaped four-armed stereo diblock poly(lactide) (4-LD) and four-armed poly(l-lactide) (4-L) polymers with different l-lactyl unit contents as low crystallizability models for the stereoblock copolymers or blends of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) were investigated. Quenching induced both stereocomplex (SC)- and homo-crystallization of non-equimolar 4-LD polymers with l-lactyl unit contents around 30 and 70%, wherein both SC- and homo-crystallization were highly prohibited in other procedures, and enhanced nucleation of 4-LD and 4-L polymers compared to the samples without quenching, resulting in formation of a large number of small-sized crystalline assemblies. The results obtained in the present study strongly suggest that the procedure of isothermal crystallization after quenching from the melt is expected to be utilized for screening the crystallizability of SC- and homo-crystallites in various types of block copolymers and blends of PLLA and PDLA and for enhancing nucleation or formation of dense crystalline structure.