**Abstract**

Evaluation of the activity of fillers for sintering composites can be obtained from the results of testing the mechanical strength, in particular, the shear strength of pitch composites. The dependence of the strength of composites on the content of fillers is described by an extremum curve. At the point of maximum strength of the composites, the optimum ratio of components is realized. At this moment, the whole pitch matrix is in the interfacial layer on the surface of the filler particles. The contact angle of fillers wetting with binders is a necessary but not sufficient condition. The activity of the fillers with respect to the particular binder is characterized by the adhesive strength of the material obtained after carbonization of the "binder-filler" system. The activity of the fillers determines caking and sintering capacity of the pitch binders. It is shown that anthracite is the most active filler for the investigated pitches. Several methods for determining caking and sintering capacity of pitches are given. One of them is the determination of these indicators by the work of destroying the pitch composites. It is shown that fillers have a significant influence on the structure of the pitch matrix in composites.

**Keywords:** filler, activity, pitch, adhesion, sintering
