Abstarct: The monitoring paitients state is one of the most important tips for curing diseases which have been put in the center of attention in last few years. It's important to know the amount of blood oxygen saturation In some cases such, operations, critical care unit and etc, that patients need fast calculation of blood oxygen and heart rate. In this thesis, any types of pulse oximeter with their advantages and disadvantages which available in markets have been introduced firstly and then the basic principles of pulse oximeter and the approach of producing a prototype will be explained. Fabricated system contains two sources of red and infrared which emitted to intended tissue respectively. Reflected or passed light from tissue is gathering by detector and by imposing processes on it, the amount of blood oxygen will be indicated. Different types of circuits is yielded and challenges was checked.