Bee distributions and their life-sustaining relationships with flowering plants occupy keystone positions in both natural and agricultural ecosystems. In Japan, the biology of Lasioglossum has scarcely been investigated. The objective of this study was to record Lasioglossum floral associations based on reference collection specimens. About 1188 specimens were identified and their floral plant species were reported. The polylectic Japanese Lasioglossum (Lasioglossum) species visit a wide range of plants; 244 species belonging to 120 genera in 53 families, and include the genera Brassica, Taraxacum, Erigeron, Ixeris, Deutzia, Leucanthemum, Fagopyrum, Phedimus, Persicaria, Hydrangea, Rudbeckia, Weigela, Salix, Crepidiastrum, Aster, and Rosa. The results revealed that Japanese Lasioglossum (Lasioglossum) species are very promising pollinators for a wide range of plants belonging to the Brassicaceae and Asteraceae families.