Purpose <p>We aimed to evaluate the effect of a 16-gauge needle as an introducer in single-operator real-time ultrasound-guided subarachnoid anesthesia.</p> Methods <p>One hundred and two parturients undergoing cesarean section were randomized to undergo real-time ultrasound-guided subarachnoid anesthesia either with (group T) or without (group C) a 16-gauge needle as an introducer. The primary outcome was the number of needle passes required for a successful dural puncture. Secondary outcomes included the number of attempts, first pass/attempt success rate, procedure time, parturients’ pain, puncture depth, periprocedural complications, and the quality of sonographic images.</p> Results <p>The median number of needle passes and attempts were significantly lower in group T than in group C [1 (1–2) vs. 2 (1–3), median difference (95% CI): 1 (0–1), <i>P</i> &lt; 0.001; 1 (1–1) vs. 1 (1–1), median difference (95% CI): 0 (0–0), <i>P</i> = 0.042]. The first pass/attempt success rates in group T were significantly higher than in group C (70.6% vs. 35.3%, 100% vs. 88.2%; both, <i>P</i> &lt; 0.001). The total procedural time was shorter in group T [108 (94–130) vs. 123 (100–163) seconds, median difference (95% CI): 15 (3–33), <i>P</i> &lt; 0.016]. No intergroup differences of pain, puncture depth, periprocedural complications and quality of sonographic images were seen.</p> Conclusions <p>The application of a 16-gauge needle as an introducer showed improved efficacy in terms of the number of needle passes/attempts, first pass/attempt success rates, and procedural time in real-time ultrasound-guided subarachnoid anesthesia.</p> Trial registration <p>The study was registered in the Chinese Clinical Trial Registry (registration date February 27, 2023 registration number ChiCTR2300068702).</p>