Viewport window in pressure hull is susceptible to high stress and can experience cracks at its corner. For studying the viewport behaviour at its corner a numerical analysis is carried out on the viewport window. The results show that the stresses are high at the corner. Furthermore, the corner of the viewport is smoothened using the fillet radius and biological growth methods. It is observed that the fillet radius method helps in reducing the localised stresses. The use of the biological growth method gives further reduction in stress. To validate the numerical results, an experimental study is conducted for viewport with fillet radius and biological growth methods. Three viewport models are manufactured and tested at 60 MPa hydrostatic pressure. The axial displacement, under hydrostatic pressure, is obtained at the centre of the viewport window of the low-pressure face. It is observed that the experimental results are in good agreement with the numerical results. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.