The theoretical background and the operation of a new dilatometric technique based on the absorption of beta particles is described. The thermal expansion of the samples is determined by their change in weight per unit area with change in temperature. The experimental accuracy in a determination of a relative change in weight per unit area is, at a counting time of 103 sec, approximately 4 × 10−5, which is close to the theoretical value. The applicability of the new device is illustrated by six runs on five different samples, among which hygroscopic and porous samples are represented. The temperature range covered is −60° to +70°C.