Abstract: Using rice allelopathy to control weeds in paddy fields is a sustainable bio-engineering technique of the 21st century. The main objective of the study was to analyze the relationship between rice allelopathic potential and its grain yield. To that end, 5 different allelopathic rice accessions (allelopathic rice of “PI-1”, “Taichung Native 1”, “Azucena”, “IAC47”; non-allelopathic rice “Lemont”) were analyzed for companion weed biomass and rice grain yield under field conditions in 2008~2010. The results indicated that weed biomass was the highest under non-allelopathic rice “Lemont” and the lowest under allelopathic rice “PI-1”. Furthermore, allelopathic rice “PI-1” had the highest and non-allelopathic “Lemont” had the lowest inhibitory effect on weed. Hence allelopathic rice “PI-1” had the highest grain yield and the reverse was true in “Lemont” under non weeding treatment. Allelopathic rice “PI-1” also had the highest while “IAC47” had the lowest grain yield under weeding treatment. The correlation analysis on weed biomass, rice allelopathic potential and rice yield indicated that grain yields of different allelopathic rice accessions were significantly negatively correlated with weed biomass while significantly positively correlated with allelopathic potential. The results suggested that allelopathic rice “PI-1” had the highest inhibition effect on paddy field weeds, the reverse was true in the case of non-allelopathic “Lemont” in the comparison of 5 different allelopathic rice accessions. Without weeding treatment, “PI-1” grain yield also exceeded those of the other rice accessions. Thus rice accession “PI-1” was the strongest allelopathic accession with the highest grain yield among the 5 rice accessions, the reverse was true in the case of “Lemont”.