The study was conducted to examine variability of green forage yield (GFY) and morphological traits (tiller length, internodes length, internodes-stem diameter, leaf width and length) in nine alfalfa varieties from USA and six varieties from Europe. The trials were carried out in Central Serbia during the second (2006-A1) and third year (2007-A2) of alfalfa exploitation. In unfavourable environmental conditions (A1), varieties from the USA had higher coefficient of variability (CV, %) in all cuttings (I CV=16.93, II CV=17.13, III CV=13.00, IV CV=21.29), as well as total yield variability (CV=14.33), compared to varieties from Europe (I CV=7.45, II CV=6.47, III CV=10.65, IV CV=19.51, for total yield CV=6.43). In the favourable agro-ecological conditions (A2) genetic potential of varieties was manifested, which caused similar yield variability. Variety origin (USA or Europe) had a low effect on variability of the morphological traits. The highest correlation (P £ 0.001) was achieved between yield and tiller length, regardless of variety origin.