Potassium ions constitute the most important macronutrients taken up by plants. To unravel the mechanisms of K⁺ uptake and its sensitivity to salt stress in the model plant rice, we isolated and functionally characterized OsAKT1, a potassium channel homologous to the Arabidopsis root inward rectifier AKT1. OsAKT1 transcripts were predominantly found in the coleoptile and in the roots of young rice seedlings. K⁺ channel mRNA decreases in response to salt stress, both in the shoot and in the root of 4-day-old rice seedlings. Following expression in HEK293 cells, we were able to characterize OsAKT1 as a voltage-dependent, inward-rectifying K⁺ channel regulated by extracellular Ca²⁺ and protons. Patch-clamp studies on rice root protoplasts identified a K⁺ inward rectifier with similar channel properties as heterologously expressed OsAKT1. In line with the transcriptional downregulation of OsAKT1 in response to salt stress, inward K⁺ currents were significantly reduced in root protoplasts. Thus, OsAKT1 seems to represent the dominant salt-sensitive K⁺ uptake channel in rice roots.