The study aims to assess the effectiveness of practices of fighting undeliberate and supporting deliberate knowledge forgetting in the companies of Russian mechanical engineering industry. The methodology of the study is quantitative, implying an econometric assessment of influence of various knowledge management practices on the effectiveness of fighting accidental organizational forgetting problems and supporting intentional organizational forgetting. Representatives of senior management of 81 companies answered a study questionnaire. Statistically significant coefficients of the regression equations of the study reveal that the knowledge management practices exert a significant influence on the perceived effectiveness of managing organizational forgetting for the chosen sample of Russian machine manufacturing companies. Namely, the practices of periodic analysis and documentation of critically important knowledge as well as of the knowledge gaps, quality control of knowledge obtained from the organization's partners, and adaptation of new knowledge to the existent exert a positive influence. In contrast, removing obsolete knowledge from practice shows a negative influence for the sample under question. The research has certain limitations of a comparatively small sample of 81 companies in one industry, which makes it possible for future research to expand samples, include other industries and/or make international comparisons. Also, a research model based on subjective perceptions can be changed toward the one based on more objective metrics, thus increasing validity and reliability of the results. On the basis of the educed results, recommendations can be developed regarding the development of preferable knowledge management practices for increasing effectiveness of managing organizational forgetting in the Russian companies of machine manufacturing and related industries. Quantitative studies comparing effectiveness of various knowledge management practices in the context of managing organizational forgetting within a specific industry are considerably rare in real sector industries not related directly to the IT and telecommunications sectors. This is especially true for Russia with its specific importance of organizational forgetting problems which arise because of the technological knowledge holders' aging. The current study is oriented to filling these research gaps.