The experimental study on the thermal-hydraulic characteristics of passive safety injection systems (PSISs) was conducted using the SMART-ITL (System-Integrated Modular Advanced ReacTor-Integral Test Loop) facility which was constructed by KAERI. The objective of this study is to investigate the effects of the flow rate of PSISs on the small-break loss-of-coolant accident (SBLOCA) scenario of the safety injection system (SIS) line break. The steady-state condition was maintained for 600 seconds before the break. When the major parameters were compared between the target value and test result, most of the thermal-hydraulic parameters agree well with each other. The water level of reactor pressure vessel (RPV) was maintained higher than that of a fuel assembly plate during the transient for the present CMT (Core Makeup Tank) and SIT (Safety Injection Tank) flow rates condition. It can be seen that the capability of an emergency core cooling system is sufficient with the PSISs of SMART during the transient.