Background: Although PICC plays a crucial role in preterm neonates, it may cause several complications. A pilot study was conducted to propose a useful equation in identifying the safe length of catheter during the first attempt of catheterization. Methods: A pilot study was carried out and NICU admitted preterm neonates requiring PICC insertion entered the study. PICC was inserted for neonates by an expert NICU nurse. After catheterization, a chest X-ray examination with contrast was done to determine the location of canola. All neonates' demographic data were extracted from medical records. Age of neonate at catheterization, the duration of catheterization period as well as data regarding the first and final sizes of the inserted PICC were also recorded. Finally, the associations between the lengths of catheters with neonates' demographic factors were assessed to propose an equation estimating the optimal length of inserted PICC. Results: One hundred preterm neonates requiring PICC entered the study. The results have shown significant associations between the first length of inserted catheter in the hand with head circumference (p=0.019; r=0.293) as well as the final length of inserted catheter in the hand with birth weight (p=0.015; r=0.304). There was a linear correlation between the length of inserted catheter in the hand with neonate's birth weight (p=0.029); however, based on the value of R2=0.167, this relationship was weak. According to these findings an equation was proposed as follows; Inserted length in hand (cm) = 17.98 + 0.618body weight (gr). Conclusion: Our results showed a positive correlation between the inserted lengths of PICC in the hand with neonate's body weight. Our findings proposed an equation; however, the regression coefficient was not significantly notable.