Lutein, one of major carotenoids in green leaves, disperses in aqueous solutions to form chiral helical aggregates which acquire an optical activity in visible region. We confirmed that this aggregate had enormous size with ultrafiltration and sedimentation equilibrium analyses. In this paper, lutein aggregates dispersed in dilute surfactant solution, SDS or DTAB, are observed with electron microscope to estimate the size and the shape of the aggregate. Lutein aggregate showed images of rod-like shape, and their sizes are from 0.3 to 1.5 um in length and from 0.05 to 0.2 um in width. Possible conformation of the aggregate with helical structure was illustrated, and a working hypothesis for physiological function of lutein in thylakoid was postulated
