Cellulose substituted by organosilicon groups represents a new type of modified cellulose. The silylation changes the physical and chemical properties of cellulose drastically. The thermoanalytical investigation of differently trimethylsilylated cellulose derivatives was carried out under static conditions in air atmosphere. The DTA curves of the cellulose used as starting material are different from those of its silylated derivatives. In the latter a new characteristic exothermic peak appears in the range 320–370°. The value of this maximum depends on the grade of silylation, being shifted towards higher temperatures with higher degrees of substitution.