Performance of Mellapak 250Y and 350Y corrugated structured packing in distillation applications at pressures ranging from 0.3 to 2.0MPa is analysed by using HTU-NTU method. These data are obtained in a distillation column with 0.15 m diameter op-erated with n-butane/n-pentane system at total reflux. In considering the axial backmixing effects, the height of an overall gas phase transfer unit, HTUOG , is divided into two parts. One part represents the height of an overall gas phase transfer unit, without backmixing, designated as*OGHTU, and the other part, designated as the height of a backmixing unit (HBUO), accounts for the backmixing effects. The HTUOG is evaluated from the measured concentration profile of n-butane in liquid phase. The HBUO obtained experimentally is correlated in terms of the properties of the materials being separated and the equivalent diameter of the structured packing. Our result shows that HBUO varies from 0.12 to 0.34 m as pressure increases from 1.0 to 1.9 MPa. It indicates that the overall efficiency of the structured packing decreases gradually at high pressure, as a result of the vapor backmixing. Performance of Mellapak 250Y and 350Y corrugated structured packing in distillation applications at ranging ranging from 0.3 to 2.0 MPa is analyzed by using HTU-NTU method. These data are obtained in a distillation column with 0.15 m diameter op-erated with n-butane / n -pentane system at total reflux. One part represents the height of an overall gas phase transfer unit, without backmixing, designated as The HTUOG is evaluated from the measured concentration profile of n-butane in liquid phase. The HBUO is experimentally in correlated terms of the properties of the materials being separated and the equivalent diameter of the structured packing. Our result shows that HBUO varies from 0.12 to 0.34 m as pressure increases from 1.0 to 1.9 MPa. It indicates that the overall efficiency of the structured packing decreased gradually at high pressure, as a result of the vapor backmixing.