Abstract： Background::Nasal insertion is the preferred method for non-intubated patients in flexible bronchoscopy; however, the relatively narrow nasal cavity results in difficulties related to bronchoscope insertion. This study aimed to investigate whether pre-operative nasal probe tests could reduce the time to pass the glottis, improve the first-pass success rate and patients’ tolerance, and reduce postoperative bleeding.Methods::This three-arm prospective randomized controlled trial was conducted in a tertiary hospital between May and October 2020. Three hundred patients requiring diagnosis and treatment using flexible bronchoscopy were randomly allocated to three groups: control group, simple cotton bud detection group (CD group), and adrenaline + lidocaine detection group (AD group). The primary outcome was the time to pass the glottis. Secondary outcomes included the first-pass success rate, the patients’ tolerance scores, and post-operative bleeding. One-way analysis of variance, Kruskal-Wallis H test, Chi-squared test, Fisher’s exact test, and Bonferroni’s multiple comparison tests were used in this study. Results::In total, 189 men and 111 women were enrolled in this study, with a mean age of 55.72 ± 12.86 years. The insertion time was significantly shorter in the AD group than in the control group (18.00 s [12.00–26.50 s] vs. 24.00 s [14.50–45.50 s], P = 0.005). Both the AD (99% vs. 83%, χ2 = 15.62, P < 0.001) and CD groups (94% vs. 83%, χ2 = 5.94, P = 0.015) had a significantly higher first-pass success rate than the control group. Compared with the control group, post-operative bleeding (1% vs. 13%, χ2 = 11.06, P < 0.001) was significantly lower in the AD group. However, no significant difference was found in the patients’ tolerance scores. Conclusions::Pre-operative nasal cavity probe tests especially with adrenaline and lidocaine during flexible bronchoscopy can significantly reduce the time to pass the glottis, improve the first-pass success rate, and reduce post-operative nasal bleeding. Pre-operative nasal probe tests are recommended as a time-saving procedure for patients undergoing flexible bronchoscopy.Trial registration::Chinese Clinical Trial Registry (ChiCTR), ChiCTR2000032668; http://www.chictr.org.cn/showprojen.aspx?proj=53321.