The purpose of the current research was to study and identify new promising pea lines with stable indicators of the trait ‘1000-seed weight’. The study was carried out in the fields of the laboratory for legumes breeding and seed production of the FSBSI Agricultural Research Center “Donskoy”, located in the southern part of the Rostov region, in the Competitive Variety Testing in 2018–2020. The objects of the study were 12 new pea lines developed by the FSBSI “ARC “Donskoy”. The standard variety was ‘Aksaisky usaty 5’. The study conducted in 2018–2020 resulted in assignment of all samples to the medium-size group, which had 150–250 g of ‘1000-seed weight’. The lines ‘B-3626/20’ (213.3 g) and ‘B-3733/9-1’ (210.7 g) produced the largest size of seeds. Intervarietal variability differed through the years. In 2018 it was 13.6%, in 2019 it was 11.5% and in 2020 it was 21.1%, with an annual average indicator of 19.8%. The analysis of intravarietal variability showed that the lowest variability (less than 10%) was characteristic for the standard variety ‘Aksaisky Usaty 5’ (5.9%), the lines ‘G-1014’ (7.7%) and ‘B-3733/9-1’ (9.1%). The average variability (10-20%) was characteristic for the lines ‘G-1008’ (13.7%), ‘B-3790/30-3’ (11.2%), ‘B-3626/20’ (19.8%). In the rest of the breeding samples, intravarietal variability was high (more than 20%) through the years of study. In this study, the standard variety ‘Aksaisky Usaty 5’ had the highest homeostasis of 157.5. Not a single new line has exceeded this figure. This indicates that this variety least of all among the studied samples, changed the size of seeds under different growing conditions through the years of study. Among the studied new breeding lines, the breeding lines ‘G-1014’ (86.3), ‘B-3733/9-1’ (64.6) had high homeostaticity due to the trait ‘1000-seed weight’.