Abstract: Mononitration of ethylbenzene was carried out with mixed acid of D. V. S. 2.66. A so far unreported dinitro-ethylphenol was isolated as lemon yellow coloured crystals, up to the amount of 0.4% by weight, from the nitration product. After being recrystallized from aqueous ethanol, it had m. p. 35 to 38°, with analysis corresponded closely to C₈H₈N₂O₅. The compound decomposed rapidly at 270°; its sodium and lead salt decomposed at 240° and 210° respectively with violence. Therefore; washing the nitration product with dilute sodium hydroxide solution prior to its distillation was suggested as a matter of safety precaution. Upon fractionation under reduced pressure, almost equal parts of o-nitroethylbenzene and p-nitroethylbenzene were obtained. Physical constants of highly purified samples were: o-isomer, n_D¹⁹ 1.5373; light absorption, maximum at 256mμ, E_1cm^1% 336. p-isomer, n_D¹⁹ 1.5458; light absorption, maximum at 272mμ, E1cm)^1% 555. The refractive index of o-nitroethylbenzene recorded in literature seemed to be erroneous.