The aim of the study was to recognise of thousand seed weight (TSW) of 44 breeding forms of Poa pratensis L. and its relationship to seed yield, leaf width, number of generative shoots, plants height, heading time. The forms of Poa pratensis including 7 cultivars, 13 breeding strains and 24 ecotypes were tested during 1997-98 in Radzików (central Poland). The forms were divided according to average of TSW in three groups: small seeds <0,300 g, medium seeds 0,300-0,350 g, and large seeds >0,350 g. Generally range of TSW was from 0,245 g to 0,425 g. The TSW of most forms was stable by years and replications. Range of coefficient variability value was from 2,4% to 15,1% for ecotypes and 4,0-6,0% for cultivars. Not significant correlation were found between TSW and seed yield, leaf width, number of generative shoots and heading time. Significant correlation between TSW and plants height was found (r = -0,40***).