Abstract: Allopathic plants release material into the soil that inhibit growth of neighbouring plants, and could affect seedling germination and growth of weeds. Many legume forages have been identified as allelopathic and inhibit the growth of accompanying plants. Lolium multiflorum has been planted widely in southern China. To study the effects on weeds, two varieties, ‘Maximus’ and ‘Hercules’ of L. multiflorum were used as donor materials. Galium aparine which was widely sown in the south of China was used as receptor material. In research on allelopathy that made full use of L. multiflorum’s allelopathy for control of weed growth, G. aparine had a very large significance. Inhibition of root extracts of L. multiflorum on G. aparine seeding germination showed a positive relation with increasing concentration, strengthening the inhibition. The inhibition of seed germination of ‘Maximus’ (-0.55) was stronger than that of ‘Hercules’ (-0.51). Inhibition of root extracts of L. multiflorum on G. aparine seedling growth had a positive relation, with an increase of concentration, strengthening inhibition (5.0%<7.5%<10.0%). The inhibition of ‘Maximus’ was stronger than that of ‘Hercules’ at the same concentration. The root extracts of ‘Maxiumus’ allelochemicals included 12 types of materials of which the main ones were acids and phenol. The root extracts of ‘Hercules’ allelochemicals included oxalic acid, methanol ethanol and butanol while the main component related to inhibition was an aliphatic compound.