Purpose: The objective of this study was to evaluate the inter- and intra-examiner reliability of ultrasonography (US) for measuring the thicknesses and cross-sectional area of the longus colli muscle (LCM) in healthy subjects. Methods: Twenty-five healthy adults participated in this study as subjects and two examiners attended to the study. LCM size was measured at the level of the thyroid cartilage. All subjects were randomly allocated to one of the three different methods. Method 1 was that the examiner A conducts the first measurement and one hour later conducts the second measurement and twenty four hours later conducts the third measurement, respectively. Method 2 was that the examiner B conducts the measurements in the same way as the examiner A. Method 3 was that the examiners A and B randomly conduct the measurements twice at an interval of one hour. Results: The intra-class correlation coefficient (ICC) for the intra-examiner reliability ranged from 0.78 to 0.98 at rest and 0.57 to 0.98 during contraction for the examiner A. The $ICC_{3,3}$ for the intra-examiner reliability ranged from 0.60 to 0.96 at rest and 0.57 to 0.92 during contraction for the examiner B. The $ICC_{2,3}$ for the inter-examiner reliability ranged from 0.80 to 0.91 at rest and 0.84 to 0.93 during contraction. Conclusion: The findings of this study indicate that US is a reliable method for measuring the LCM size.