Electrical and interfacial properties of Sn/Methylene Blue (MB)/p-Si Schottky diode have been determined by using current-voltage (I-V) and capacitance-voltage (C-V) measurements of the device at room temperature. Cheung functions and modified Norde functions have been used to obtain the electrical characteristics such as barrier height and series resistance of the diode. It has been seen that the MB layer modifies the effective barrier height of the structure because the layer creates the physical barrier between the metal and the semiconductor. Electrical properties of the device obtained from C-V characteristics have been compared with the ones obtained from its I-V characteristics. It has been seen that at sufficiently high frequencies, the charge at the interface cannot follow an ac signal. The interface state density of the diode has been also calculated. (C) 2009 Elsevier B.V. All rights reserved.