The objective of this study was to evaluate the nutritional value of Spirodela polyrhiza (L. Schleiden) (greater duckweed, GD) by analysing its chemical composition, mineral content and amino acid profile under laboratory conditions. GD was cultured in an aquarium illuminated from 04:00 to 24:00, maintaining a water temperature at 25 °C and a pH range of 6.5–7.3. The plants were collected, dried and ground for analysis. The content of crude protein, fat, ash, fibre and starch of GD was (% dry matter): 31.3, 5.7, 17.9, 10.5 and 7.8, respectively. The content of total amino acids, essential amino acids and nonessential amino acids was (g/100 g crude protein): 76.6, 36.5 and 40.1, respectively. The total content of minerals, macronutrients and trace elements in GD biomass was (g/100 g crude ash): 34.3, 34.2 and 0.1, respectively. In summary, our data indicate that Spirodela polyrhiza has a high content of crude protein and ash as well as significant amounts of amino acids and minerals. This suggests that GD could potentially be a valuable source of these nutrients for both animals and humans.