In this study, variation regarding the days from sowing to 50% flowering stage (FL); dry weight at 50% flowering stage (DW); and contents of crude protein (CP), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), acid detergent fiber (ADF), neutral detergent fiber (NDF), and dry matter digestibility (DDM), dry matter intake (DMI), relative feed value (RFV), Ca/P ratio and K/(Ca+Mg) ratio characteristics in hay were investigated in 56 grass pea (Lathyrus swims L.) accessions comprice of 51 Turkish landraces, one released variety 'Gurbuz-2001', and 4 ICARDA lines (560, 564, 565, 566) in 2007-2008 and 2008-2009 growing seasons. Number of the days to 50% flowering was between 174 and 184, and plant dry weight was between 7.63 and 25.52 g amongst grass pea accessions. The range in hay was 20.95 - 26.31% for CP, 28.80 - 34.40% for ADF, 33.42 - 45.01% for NDF and 129 - 185 for RFV amongst accessions. In general, while hay of landraces had higher CP, Ca, Mg, K and P content and RFV than ICARDA lines and released variety, the earliest accession was Gurbuz-2001 variety. Landraccs N2, D1 and BR1 were the most promising accessions for hay production or breeding for their CP, ADF, NDF contents, RFV value and yield.