Objective: The present study aimed to validate the SSSL in pre-determinating the insertional length between the sixth and tenth thoracic vertebrae (T6-T10) and examine repeatability property. Material and Method: A prospective recruitment of 52 babies who were placed the umbilical arterial catheter in the NICU, Thammasat University Hospital was performed. Insertional length of the distance between suprasternal notch and superior iliac spine (SSSL) were performed. The catheter tips were verified against anatomical points on chest and abdominal radiograph. The SSSL was measured twice on each patient to indicate repeatability property. Results: All babies (100 percent accuracy) were correctly placed the catheter tips at high placement (T6 to T10) at the first attempt. Repeatability coefficient for repeating measure of the SSSL was 0.7 centimeters. Conclusion: The SSSL is repeatable, simple, and perfectly accurate for pre-determination of the umbilical arterial catheter length to position the catheter tip at T6 - T10.