Description: In a general view the expert error can be defined as inappropriate to the objective reality judgement of the expert or his action which do not lead to the solution of problems of expert research, or erroneous judgement which represent result of a diligent error. It distinguishes an expert error from a crime against justice which the expert can make. The problem of expert errors is practically undeveloped. The correct solution of a problem depends on possibilities and readiness of experts (I.Q., knowledge, skills and abilities, other features of the expert personality). At the same time the reason of an erroneous conclusion of the expert is not always a consequence of wrong actions of the expert. His research can be carried out faultlessly, and the drawn conclusions entirely correspond the received results, but if the initial data for examination were erroneous or investigated objects forged, etc., the conclusion of the expert in aspect of truth establishment in the case will be erroneous.