In this study, the influence of chemicals in surrogate gasohol on physical, thermal and mechanical properties of glass fiber reinforced nylon 6 (PA6) composites were investigated. Test specimens of neat PA6 and PA6 compound with 15%wt and 30%wt glass fiber were prepared by compression and injection molding machines. These specimens were immersed in isooctane, toluene, aggressive ethanol, and ethanol at room temperature for 16 weeks. The chemicals were changed every 6 weeks. Mass and dimensional stability, heat distortion temperature (HDT), glass transition temperature (Tg), tensile, flexural, compressive and Izod impact properties were investigated. The results showed that the glass fiber provided dimensional stability by restricting the movement of polymer chains. The glass fiber could improve the tensile strength, tensile modulus, flexural strength, flexural modulus, compressive strength and Izod impact strength of PA6/GF composites due to good interfacial bonding between PA6 and GF and stress could transfer to glass fiber. Ethanol and aggressive ethanol significantly affected the physical, thermal, and mechanical properties of neat PA6 and PA6/GF composites more than isooctane and toluene because they could be absorbed into PA6 matrix easier. The thermal and mechanical properties except Izod impact strength of specimens decreased with increased amount of chemicals absorbed. But the effects were reduced in the PA6/GF composites because the fiber glass could reduce the movement of polymer chains. Overall, the effects of gasohol on properties of PA6 were mainly from alcohol component than gasoline component. Therefore, PA6 and PA6/GF composites should be used with gasohol with low ethanol volume content.