In this laboratory work, several types of clays have been considered as additives to the bentonite and sepiolite mixtures that are used as drilling mud-making colloids for high temperature stability. To develop suitable mud composition resistant to high temperature, several experiments were conducted on sepiolite samples of different compositions taken from Eskisehir region of Turkey. Mud compositions were obtained with different combination of sepiolite clay and other materials. Rheologic and filtration properties of these compositions were determined under room conditions. Additives with high temperature stability were added to these muds and they were aged at different temperatures. Afterwards, the changes in their rheological behavior and filtration properties were observed when the mud was exposed to high temperature. Finally, three prototypes of mud were developed and their properties were reported.