In agriculture, weeds are mostly managed by the synthetic chemicals since rapid results. However, the use of chemical herbicides may also pose questions about their potential health impacts and environmental effects. This study was aimed at screening the inhibitory effects of Chrysanthemum indicum (CI) flowers on plant growth using Lemna phytotoxicity assay. Dried flowers of CI were serially extracted with methanol and water (for aqueous extract, the marc from the extract is repeatly extracted with methanol). All of three extracts (methanolic extract, aqueous extract and methanolic extract of marc from water extract) were used to test if they exhibited inhibitory effects on duckweed (Lemna minor) growth compared with negative control in the tested model. The inhibition activities of extracts were determined by serial dilutions of each extract and expressed as effective concentration that resulted in 10% (EC₁₀) inhibition of duckweed growth which is appropriate value to evaluate this inhibitory effect. Our results showed that the extracts resulting by using methanol as extracting solvent had the greatest inhibitory effects. Methanolic extract and methanolic extract of marc from water extract had EC₁₀ of 227.44 and 212.22 µg/ml respectively. On the other hand, aqueous extract of CI was shown to have the least inhibitory effect (EC₁₀ = 277.68 µg/ml) on duckweed growth. A phytochemical screening showed rather similar pattern of chemical compositions in methanolic extracts and methanolic extract of marc from water extract, the major one is phenolic compound of flavonoid glycoside. As expected, aqueous extract was shown to contain no other phytochemical except sugars and phenolic group moiety structure. The study is worthy of further investigation since this may bring waste (marc of CI after aqueous infusion) to be used again as value-added if we can lead to the discovery of new effective, safe and applicable bioherbicide from them.