The volumetric change (thermal expansion or thermo-swelling) of Kukersite oil shale, which contains thermo-softening organic matter, was measured up to 1,000 °C using a spring loaded linear velocity displacement transducer under inert pyrolysis conditions. The research was focused on examining the thermal swelling taking place in the thermoplastic stage of pyrolysis. A heating rate of 10 °C min-1 was applied to evaluate general trends of volumetric change. The materials studied were commercial grade oil shale with 30 mass/% of organic matter content (oil shale with about 190 L t-1 oil yield) and concentrated kerogen with 88 mass/% of organic matter content (or about 600 L t-1 oil yield). The concentrated kerogen has an organic content similar to that of many coals. The present study indicates that during pyrolysis under retorting conditions, the organic matter of Kukersite oil shale itself can, in principal, exhibit short-term thermal swelling (or dilatation) that accompanies extensive volatiles evolution. However, in the case of the commercial grade oil shale, this phenomenon was not observed due to the low organic matter content of this oil shale.