The aim of the presented studies was to evaluate the effect of cultivar and various sowing dates on the quantity and quality of protein in the seeds of narrow-leaf lupine. We used seeds obtained from plot experiments carried out during 2005. The experiment was carried out in a split-plot / split-block design. The primary treatment was represented by cultivars of thermo-neutral and non-thermoneutral lupine, while sowing dates (I – very early; II – two weeks following the first date; III – four weeks following the first date) were the secondary treatments. Using a near-infrared spectrometer, we measured the content of total protein and its amino-acid composition in lupine seed. The results were processed statistically by means of two-factorial ANOVA (cultivar x sowing date). Significant (P ≤ 0.01 or P ≤ 0.05) differences were found between the cultivars in total protein content and protein amino-acid composition (in g•100 g-1 of protein). Moreover, a significant (P ≤ 0.05) effect of sowing date on total protein content in dry matter of the seeds was found.