The thermal-hydraulic research supporting the development of an integral type of reactor named System-integrated Modular Advanced ReacTor (SMART) is discussed. First, the SMART development program is introduced. The Standard Design Approval (SDA) for SMART was certificated in 2012 based on extensive technical validation activities during 2009 to 2012, and a set of passive safety systems (PSSs) was designed and validated for SMART during 2013 to 2015 after the Fukushima Daiichi accident. During 2016 to 2018, the Kingdom of Saudi Arabia and Korea conducted a 3-year project of Pre-Project Engineering (PPE), and now, the Standard Design Approval (SDA) for SMART100 is being processed from 2019. Second, the SMART validation test program and related test facilities are introduced. A set of integral effect tests (IETs) was performed using VISTA-ITL, and several separate effect tests (SETs) using the facilities of SWAT, SCOP, and FTHEL were performed for SMART SDA. Counterpart tests for SMART SDA were performed with the newly constructed SMART-ITL facility, and various validation tests for SMART PSSs were also performed. In addition, dozens of validation tests for SMART PPE were performed to produce IET data for design-basis-accident scenarios and PSSs. Additional SETs for SMART PPE and SMART100 SDA were performed using the facilities of SISTA-1, SISTA-2, and FINCLS. Third, the major test results are discussed for phenomena expected to occur in an integral type of reactor such as the SMART design. They include core cooling behaviors in the reactor coolant system and safety injection behaviors in the passive safety injection system and counterpart test results of a small-break loss-of-coolant accident between VISTA-ITL and SMART-ITL. Fourth, the major analysis results for SMART are discussed. Several sets of code analysis were performed for selected IET cases with the MARS-KS and TASS/SMR-S codes to validate their models and the codes themselves. They include simulation of a SMART safety injection system line break test with the MARS-KS code, validation of the TASS/SMR-S code for natural circulation tests, and validation of the MARS-KS and TASS/SMR-S codes based on a pressurizer safety valve line break test.