<p>Detecting vegetable oils’ edibility and their oxidation state using a simple, fast, and easy method that can be used by non-experts and ordinary consumers has always been challenging. The currently used methods in assessing oil oxidation and deterioration are expensive, complicated, and only scientists are qualified to deal with them.This work aims to monitor the oxidation of sunflower and corn oils using a visual colorimetric method. This approach is based on biofilms of agarose and polyvinyl alcohol (AGR/PVA) impergenated with Congo red dye. Hydroxylamine sulfate (S) or chloride (C) were also used to prepare two types of biofilms (AGR/PVA/S and AGR/PVA/C). These chemicals react with the aldehydes emitted from oxidized oils, causing a pH decline and hence a change in the dye’s color from red to blue. Oil oxidation was induced by heating at 65&#xa0;°C for 35 days. The oxidized oils were evaluated for their stability, fatty acids composition, and hexanal content as a representative aldehyde. Through calculating color difference (ΔE), both types of biofilms were effective in detecting oil oxidation. But, AGR/PVA/S was more visually effective (ΔE = 33.65) through a gradual color change than AGR/PVA/C (ΔE = 21.03), especially in sunflower oil after 35 heating days. Also, ΔE of both biofilms (AGR/PVA/S or C) had strong Pearson’s correlation coefficient (R² ≥ 0.9) with all oxidation parameters of sunflower oil, making biofilm highly expressive for the oil’s oxidation state. Therefore, the investigated biofilms could be strong candidates as an easy, reliable, and fast oil oxidation detection device.</p>