Calcified Nuia is a problematic microfossil with a distribution range limited to the Early Ordovician. Its affinity has long been controversial due to the absence of morphological details as for an eodiagenetic taphotaxon. Here, we investigate a collection of Nuia is identified in the patch reefs at the top of the Honghuayuan Formation (Floian Stage, Early Ordovician) in northern Guizhou. Thin section investigations along with Raman spectroscopy (RAM) and scanning electron microscopy (SEM) reveal an unexplored pathway for its morphological deconstruction and calcification mechanism. Nuia is featured here as an irregular thallus colony surrounded by an external calcified encrustation and with densely filaments radially arranged from the dark central area that corresponds to the emplacements of heterocysts and/or aktinetes on the base of the filaments. We, therefore, temporarily assign Nuia to an early taxon of Rivulariaceae (Nostocales, Cyanophyta). Integrating the model of vivo cyanobacterial calcification by carbon dioxide concentrating mechanisms (CCMs)- enhanced photosynthesis, we propose a calcification process of Nuia to be as follows: at the beginning, calcium carbonates induced by CCMs deposit in the base sheaths of initial filaments, forming a black central area of Nuia; as the trichomes grow and produce false branching, seasonal pattern of growth and calcification is formed in zones where the filaments develop false branching, appearing as unique multilayers. When the trichomes stop growing, an outer common sheath formation and CCMs- induced precipitate of calcites is formed on the surface of colony by impregnation and/or encrustation, and the filaments are rapidly metasomatized by calcite fibers during early diagenesis. In addition, residual organic macromolecules probably gathered in the central area and the common sheath, limit the rapid growth of crystals and eventually form tiny calcite minerals during the calcification process and, furthermore, make them darker than the calcified filaments and the surrounding rocks.