Interaction between fluids and solid surfaces plays important roles in many fields, e.g.: enhanced oil recovery (EOR), environmental engineering, agriculture, materials, etc. Research on this topic is intensively carried out by many researchers. In this research, a simple experimental setup for fluid contact angle measurement is constructed using an optical microscope and video camera with 29 frames per second. Measurement of contact angle of fluid with variation of salinity, i.e.: 1M, 2M, 3M, 4M, and 5M is carried out by recording a single droplet placed on a rock surface. Each frame of the recorded video are then analysed using image processing technique to detect the edge and calculate the contact angle. A single 8th order polynomial was applied to the edge of the wetting type droplet, but two types of polynomial fitting curves are applied for edge of non-wetting type droplet. It is obtained that on preparatory glass, the higher the molarity, the longer the droplet will evaporated. On the sandstone surface, fluid contact angle on sandstone surface is about 80° and decreases with time with different trend of decrement. This may be due to complex interaction between fluid and pores at sandstone surface spot.