The study was conducted between 2007-2009 years in educational and experimental base of the Agricultural University - Plovdiv. The observations were made in the field trial, which is set by the method of fractional plots in four replications.Considered entry into the main phenological phases of two Bulgarian variety (Obrazcov chiflik 4, Mina), one American (HiFi) and one Serbian (Novosadski naked). There have been specific correlation between the length of the period between the phases and the amount of precipitation in the period. It was found that precipitation during different phases of development of spring oats strongly influence the duration of the inter-phase periods expressed by correlation coefficients (during the period between sowing to germination - R = 0,898; during the interphase period third leaf - tillering - R = 0,993 to R = 0,998; during the interphase period tillering– stem elongation - R = 0,547 to R = 0,698; during the interphase period stem elongation - flowering -R = 0,830 to R = 0,999). The relationship between the amount of precipitation after flowering till the end of the vegetation and the duration of interphase period flowering - full maturity is slightly negative in all tested varieties. A similar trend is in the period from germination to stage third leaf. Between varieties not reported significant differences. The total amount of precipitation during the growing period and the reported length of the growing period is in a strong negative correlation (R = -0,800 to R = -0,985)