Surface roughness is an important factor when dealing with biomedical implants, which defined an artificial organ used for restoring the functionality of a damaged natural organ or tissue of the human body . It can be measured in different methods: stylus instruments, optical instruments, scanning tunneling microscopy and atomic force microscopy. Optical methods used for measuring the surface roughness, by measuring the change of voltage according to change of materials surface. In the optical system, the distance of materials will change to give an output voltage by put the laser light on the surface of material and collect the reflected ray from the surface to the electrical circuit. In this research an electrical circuit was designed using an operational amplifier and a photo-transistor to measure the change in resistances. The operational amplifier is used for amplifying the signal coming from the receiver because this signal is very small in micrometer and a phototransistor is considered as a sensor for the signal . The electrical circuit properties are simulated using Multisim 8.3 by Electronics Workbench program and the results of this simulation was compared to the experimental results which implied that this circuit was reliable to detect the surface roughness of many types of materials .