A pressurizer is a major component used to control a system pressure in a primary coolant system of a pressurized water reactor. To identify the system pressure characteristics on nitrogen gas-water and steam-water pressurizers for an integral pressurizer water reactor, an experimental study is carried out on the integral test facility, VISTA-ITL, which is a scaled down facility of the SMART plant. According to the experimental results, the pressurization rate and peak pressure are affected by the pressurizer type. The pressurization and depressurization rate with the steam pressurizer is smaller than the gas pressurizer since water has its inherent characteristic having latent heat while a nitrogen has ideal gas properties. The safety valve in both the gas and steam pressurizers is not opened during the transient. It is one of the characteristics of the integral reactor SMART design with a large pressurizer volume. The cooldown rate of the primary coolant system during the later part transient depends on the decay heat level regardless of the pressurizer type.