1. Pronamide treatments showed slight crop injury at initial stage of alfalfa but recovered rapidly by growing stage progressed. No significant differences of plant height were observed at 50 days after seeding (Jun 1) among the dosage levels of pronamide. But a significant difference at the 5 % level of plant height were observed among the number of application of pronamide and interrelation of dosage x number of applications at 70 days after seeding. 2. Bet ter weed control effect was observed at higher dosage level or more applications number of pronamide (p$lt;0.01). Pre-emergent application was more effective for weed control than late post-emergent application at 30 days after seeding. 3. Higher yield (dry weight) of alfalfa was harvested with the three applications of R₂ (150g/l0a) dosage level, two applications and post-emergence application of R₃ (200g/l0a) dosage level. Lower yield of alfalfa was harvested with the one application at pre-emergence compared with two or three applications at pre post-emergence stage and one application at post-emergence stage (P$lt;0.01). 4. Significantly lower weed dry weight was obtained at higher dosage level of pronamide than untreated control (P$lt;0.01). But a higher dry weight of weed was harvested with the one application at post-emergence stage compared with pre-emergence application (P$lt;0.01). 5. Major weeds grown in the test field were Digitaria sanguininalis, Chenopodium album, Amaranthus mangostanus, Calystegia japonica, and Cyperus difformis. Digitaria sanguininalis which was the major problem weed was almost completely controlled by two applications of. R₂(150g/10a)dosage level, but the same dosage was not as effective with gyperus difformis.