Twenty percents of the oil in the reservoir is typically produced naturally through the reservoir pressure. In order to produce residual oil in the reservoir when the reservoir pressure is dropped, third methods of enhanced oil recovery are carried out. In recent years, due to the lifespan of most of the world apos;s oil wells and their entry into the second half of their life, rising oil prices and the growing need of countries for fossil fuels, the choice of third appropriate method in order to recover the residual oil from the reservoir is very important.Today, the use of chemical surfactants for reservoir flooding is a common practice. But due to the high cost of producing and using chemical surfactants and their environmental pollution, oil companies are interested in finding better and less polluting methods. The use of bacteria for enhanced oil recovery is not a new method and has been used since many years ago. These days, because of the advancement of biotechnology and the ability of bacteria in the production of bio-surfactants resulting to the ability of enhanced oil recovery from reservoirs and the lack of environmental contamination, the use of microbial enhanced recovery techniques has been considered. This study investigates enhanced oil recovery by Bacillus Persicus bacteria and the mechanisms affecting the microbial enhanced recovery using Plexiglass micromodel. In order to compare microbial enhanced recovery with other methods, the micromodel was flooded by water and SDS surfactant injected into the micromodel. Bacillus Persicus bacterium is a native bacterium in Iran and its growth chart was extracted for the first time. A Plexiglass micromodel which is a traarent polymeric and oil-wet material, has been constructed and used for the first time in this research. With taking pictures of changes within the micromodel, the images are analyzed by calculating the change in the number of black pixels in each image by MATLAB software, the amount of enhanced oil recovery is calculated. Tests are carried out to determine the effective mechanisms in enhanced recovery by Bacillus Persicus bacteria. Experiments show that injection of bacteria into a porous media of micromodel containing oil led to 65% of enhanced oil recovery, while water and SDS-containing solutions failed to penetrate into the matrices and remove the oil trapped in the matrices. In the test of interfacial tensile change measurements between bacterial and oil-based solutions, we found that the bacteria could reduce the interfacial tension by 21%. The bacteria also reduced the viscosity of oil by 53% because of producing gas. The placement of bio-surfactant on the surface of the Plexiglass has led to a change in the wettability of surface from oil-wet to water-wet. Keywords : MEOR, Bacillus Persicus, Plexiglass Micromodel, Interfacial Tension, Viscosity, Wettability, SDS Surfactant