The basic ingredients for making medical devices are varied, so they require different sterilization techniques. Sterilization techniques that do not cause heat are needed because not all medical devices are made from heat-resistant materials. This study aims to develop a mathematical model of deactivation of biofilm-forming bacteria with a combination of electric fields and light. Mathematical models are used to explain the mechanism of the decrease in the number of bacteria on biofilms. The mathematical model testing was only carried out at the electric field intensity of 2.5 - 4.0 kV / cm and the light intensity of 50 - 250 mW / cm 2 and in the biofilm of the bacterium Pseudomonas aeruginosa. The pulse duration of the electric field used is 50 µs, while the wavelength of light is 405 nm. Biofilm originated from the bacterium Pseudomonas aeruginosa grown on a catheter and incubated for 6 days at 37oC. Biofilm exposure was carried out at room temperature 30oC and environmental air humidity around 75%. The results showed that an increase in the electric fields and light caused an increase in the decrease in the number of bacteria. Decreasing the number of bacterial colonies that occur fulfills logarithmic functions. The decrease in the number of bacteria is caused by an increase in the amount of diffusion of water and ions that pass through the cell membrane, thereby damaging the cell membrane. Increased diffusion of water and ions that pass through the membrane occur because of the modulation of the external electric field with the electric field of the charge space produced by light. The electric field of space charge does not affect the occurrence of irreversible electroporation.