This paper examines the strength characteristics of Portland cement-treated fat and lean clays (CH and CL) under the conditions of freeze-thaw cycles. Specimens of natural clays were mixed with Portland cement in different percentages of 5% and 10%, in terms of the dry mass of soil using two different water contents of 30% and 50% for CH type of clay soil and 20% and 30% for CL type of clay soil to represent different consistencies and workability of soils. Besides, a group of cement free specimens was prepared and/or a group of specimens was not subjected to freeze-thaw cycles for comparison reasons. All specimens were cured for 7 and 28 days in a humidity controlled room at a constant temperature. After curing, specimens were subjected to a maximum of five cycles of closed-system freezing and thawing. Unconfined compression tests and ultrasonic pulse velocity tests were conducted on the specimens. The results of unconfined compression tests were evaluated in terms of water-cement ratio, curing period and the number of freeze-thaw cycles. Consequently, the compressive strength increased with the cement content increment of the clay specimens. While the specimens with highest cement content showed brittle behavior before freeze-thaw tests, they manifested less brittle behavior after freeze-thaw tests. The highest strength values were obtained in the specimens with low water contents. The compressive strength decreased as the freeze-thaw cycles increased, but cement treatment partially prevented the strength loss in freeze-thaw conditions. Generalized equations of strength development were assessed considering the total water-cement ratio and curing time effects for fat and lean clays that were subjected to 0, 1, and 5 cycles of freeze-thaw tests. In this way, this study showed that clay water-cement ratio hypothesis can be used to analyze the strength development of clays at different freeze-thaw cycles. It was observed that a linear correlation existed between the ultrasonic pulse velocity and the unconfined compression strength values. Furthermore, the plasticity index of the specimens subjected to 5 freeze-thaw cycles showed a decrement for the clay which was highly plastic in its native condition. Finally, with this study it is proven that cement treatment techniques can be preferred to enhance the freeze-thaw durability of fat and lean clay soils. (C) 2015 Elsevier B.V. All rights reserved.