The vapour-liquid condensation phenomenon in a pressure tank in a thermally stratified state was experimentally investigated. Vapour under designated conditions was injected into the pressure tank, which contained low-temperature test fluid (R290) in a saturated liquid state, for identification of the condensation phenomenon in the thermal stratification state. The vapour-liquid condensation phenomenon was qualitatively and quantitatively analysed by investigating the heat and mass transfer. The vapour injected was partially condensed, yielding a non-equilibrium state between the vapour and liquid inside the tank. Further, a temperature stratification phenomenon occurred between the upper and lower regions of the liquid. This non-equilibrium state constituted a different result to that for vapour-liquid condensation obtained through thermodynamic modelling assuming an equilibrium state. The factors affecting the vapour-liquid condensation phenomenon included the mass and initial pressure of the liquefied inventory in the test cell, along with the pressure, and flow rate of the inlet vapour flow. Thus, the vapour-liquid condensation phenomenon was experimentally clarified in this study by setting those factors as variables. Four sets of experiments were performed to confirm the effect of each variable. The higher the enthalpy of the inlet vapour flow, the faster the pressure rose. Further, a higher pressure corresponded to a lower energy requirement for condensation. A lower initial energy of the liquid region in the test cell corresponded to a faster condensation rate, and the liquid level fraction did not affect the condensation rate. Mathematical modelling predicted the pressure behaviour to within a 8% error.