Three new chromones, 2-(3-hydroxypropanoyl)-8-methoxy-5-(2 oxopropyl)-4H-chromen-4-one (1), 8-hydroxy-2-(3-hydroxypropanoyl)-5-(2 oxopropyl)-4H-chromen-4-one (2), 2-(2-hydroxyethyl)-7-methoxy-5-(2 oxopropyl)-4H-chromen-4-one (3), together with four known chromones (3-7) were isolated from the twigs of Cassia fistula. Their structures were determined by means of HRESIMS and extensive 1D and 2D NMR spectroscopic studies. Compounds 1-3 were tested for their anti-tobacco mosaic virus (anti-TMV) activities. The results revealed that compounds 1-3 showed high anti-TMV activities with inhibition rates of 26.6, 28.2 and 29.7%, respectively. These rates are close to that of positive control.