Abstract-A study of the calculation of pleural effusion index (PEI) in patient with dengue hemorrhagic fever (DHF) has been conducted. PEI calculation was done through matlab programming language. Some digital image processing methods used in this research were thresholding segmentation, morphology operation, and calculation of pixel number per column in image to get PEI value. PEI values generated from image processing can be an alternative to replace the manual calculations done by physicians and used to demonstrate the gravity level of DHF.