Since August 2006, each airline passenger has been allowed to carry only a maximum of 100 ml liquid in each container and a total of not more than 1,000 ml in carry-on luggage. This measure was adopted to prevent bringing sufficient amount of deleterious liquids such as flammable, combustible and explosive liquids into the aircraft. Several methods have been investigated and tested to screen liquids in bottles at airports but none of them has been accepted as a routine inspection method. This research introduces low energy X-ray/gamma-ray transmission technique using a small ²³⁸Pu isotopic source and a compact 25 mm³ CdTe detector. The linear attenuation coefficients of various kinds of liquids contained in bottles having different sizes and thickness at 13.6 – 43.5 keV were determined without measurement of transmitted X-rays from an empty identical container or the empty portion of the container. Attenuation factor of the container was obtained from the estimated or measured container thickness and the predetermined linear attenuation coefficient of the container material. The technique introduced here could clearly distinguish alcohol, fuel oil and other kinds of liquid from water contained in bottles and cans while its sensitivity is dependent upon radiation energy and diameter of the bottle. It could be concluded that the proposed method has potential application in screening liquids contained in bottles for aviation security but further investigation on using other X-ray sources and X-ray detectors is recommended.