Abstract: Unilateral spinal anesthesia is used to limit sympathetic, sensory and motor blocks and minimize hemodynamic changes. This study aimed to assess the effect of unilateral spinal anesthesia on patients with lower limb surgery when they were kept in the lateral decubitus position for 10, 15 and 20 min. We observed the effect of hyperbaric bupivacaine (0.5% of 10 mg) on sensory block, motor block and hemodynamic stability. This single-blind, randomized clinical trial was conducted on 51 subjects divided into 3 groups (each consisted of 17 subjects). Each group received spinal anesthesia (with the surgery side down) using hyperbaric bupivacaine (0.5% of 10 mg). Bevel was directed toward the surgery side and the injection was given slowly over 60 seconds without barbotage. After administration of spinal anesthesia, the lateral decubitus position was maintained for 10 min in group A, 15 min in group B and 20 min in group C. After that, patients returned to the supine position and block onset, duration and height and the patients’ hemodynamics were assessed. The findings of this research revealed that there was no significant difference in the onset of sensory and motor blocks, nor on the height of the sensory and motor blocks on the surgery side (p<0.05). The height of the sensory block on the independent side was Th12 (group A), L3 (group B) and S1 (group C). The duration of the sensory block on the independent side was 71.47±10.4 min (group A), 63.53±4.9 minutes (group B) and 50.59±13.4 min (group C). This showed significant difference (p<0.05). The duration of the motor block on the independent side was 109.41±18.2 min (group A), 84.71±33.9 min (group B) and 7.06±19.9 min (group C). This also showed a significant difference (p<0.05). Unilateral motor block was 88.2% in group C and 11.8% in group B; however, it was not achieved in group A. The three groups showed hemodynamic stability in mean arterial pressure and heart rate. Lateral decubitus position lasting 10, 15 and 20 min after unilateral spinal anesthesia had different influences on sensory and motor blocks on the independent side.