Simultaneous exposure of highly-used chemical and physical agents are expected to happen in many occupations. In the present study the impact of simultaneous exposure to noise and formaldehyde on oxidative stress in blood and liver tissue of rat was investigated. Animal study was conducted in the School of Public Health, Shahid Beheshti University of Medical Scineces, Tehran, Iran in 2013. A total of 42 male Wistar albino rats were randomly divided into 6 groups (7 in each group). Rats in control group were not exposed to any stressor, while 2 groups were exposed to 6 and 12 ppm formaldehyde, 1 group to noise (0.7–5.7 kHz, 100 dB SPL) and 2 groups to noise + formaldehyde (8 h/d, 28 days). The level of oxidative stress in blood and liver tissue were determined through GSH and MDA measurements. Sound pressure level was monitored using a calibrated Bruel and Kjaer 2238 sound level meter (Denmark). Formaldehyde concentration was monitored four times an hour by a photo ionization detector (Photocheck +5000, Ionscience Co., UK). GSH concentrations were measured through titration and quantification of thio-nitro-benzene using spectrophotometry at 412 nm. MDA levels were quantified by absorption at 535 NM wavelengths using a spectrometer. The results revealed that exposure to both stressors significantly reduced the GHS levels and significantly increased the MDA levels in exposed rats. The level of changes in groups with simultaneous exposure was dose-dependent (p<0.05). The current study clearly confirmed that co-exposure to noise & formaldehyde has an additive effect in oxidant /antioxidant system imbalance.