A search for agrochemicals from Hyptis suaveolens Poit., a weed in the family Labiatae, led to the isolation of thirteen substances. Eight substances isolated from crude dichloromethane extract included a mixture of two steroids (HS-1), oleanolic acid (HS-2), 4’,5-dihydroxy-7-methoxy flavones (HS-3), 5-hydroxy methyl furfuraldehyde (HS-4), a mixture of two steroids glycoside (HS-5), a mixture of two triterpenoids (HS-6), mixture of long chain alcohols (HS-7) and a mixture of long chain esters (HS-8). While five additional compounds, namely, β-amyrin (HS-9), α-amyrin (HS-10), lupeol (HS-11), betulinic acid (HS-12) and ursolic acid (HS-13) were isolated from crude hexane extract. 4’,5-dihydroxy-7-methoxy flavones (HS-3) and 5-hydroxy methyl furfuraldehyde (HS-4) had not been reported as constituents of this plant. In the study of plant growth inhibitory activity against seedling Echinochloa crus-galli Beauv., it was found that 5-hydroxy methyl furfuraldehyde (HS-4) showed the highest inhibitory activity at 82% at 1000 ppm, followed by betulinic acid (HS-12) and 4’,5-dihydroxy-7-methoxy flavones (HS-3), which gave 52% and 45% inhibitory activities, respectively. Furthermore, seedling growth inhibitory effect against selected seedling plants: Lactuca sativa Linn., Trianthema portulacastrum Linn., Bidens pilosa Linn., Brassica Chinese Jusl., Dactyloctenium aegyptium Willd. And Pennisetum polystachyon Schult. were also investigated. 5-hydroxy methyl furfuraldehyde (HS-4) exhibited the highest inhibitory effect activity against root growth on these other plants.