Chiral organic materials are rapidly emerging as apromising platform for circularly polarized lasing. However, the lag inmechanistic research has severely hindered the development oforganic circularly polarized lasers. Here, we attempt to probemultilevel chiroptical activity in organic supramolecular microcrystalsfor exploring high-performance circularly polarized lasing. Theevolution of chiroptical activity is tracked spanning from chiralmolecular monomers to dimers to supramolecular helices. Thecrucial roles of excimers and supramolecular helices in achievinghigh optical gain and large chiroptical activity are revealed.Accordingly, circularly polarized lasing with low thresholds and largedissymmetry factors is realized in the organic supramolecularmicrocrystals. Our work marks the beginning of mechanisticresearch on chirality induced circularly polarized lasing, which willinitiate the rational design of chiral organic materials for circularlypolarized lasing