Carbon nanodots (Cdots) have excellent luminescence property and simple preparation process so they continue to be developed today. Cdots can be prepared via thermal treatment from natural organic materials, such as plants containing biologically active compounds (BACs) of secondary metabolites. BACs also exhibit luminescence property, which can contribute to the luminescence of the Cdots. This is a preliminary study aimed to study the luminescence in the formation of Cdots via extraction of thermally treated Water Apple leaf wastes and dried Sappan wood using distilled water as the solvent. Furthermore, we would like to know whether the formation of the Cdots is achieved by observing the ultraviolet-visible (UV-Vis) absorption spectra of the samples obtained. The thermal treatments in this study are drying under sunlight, roasting, and oven heating. The precursors used are organic solid materials of Water Apple (Syzygium aqueum) leaf wastes and dried Sappan (Caesalpinia sappan L.) wood. Each thermally treated solid sample is dissolved in distilled water and filtered. Sample characterization is carried out via UV/violet laser exposure and UV-Vis testing to study the luminescence of the samples. The results show that under visible light the appearance of the samples changes from yellow and/or brown (BACs) to colorless as the Cdots are formed. Exposing an UV/violet laser upon the samples produces luminescence that changes from whitish-green to cyan and whitish-yellow to blue for Water Apple leaf wastes and dried Sappan wood, respectively, as the Cdots are formed. Changes of the UV-Vis absorption spectra are also exhibited in the formation of the Cdots, i.e. the absorption value reduces and the number of peaks decreases.