Nowadays, the Ukrainian economic system is facing difficulties because of country's integration into the world globalization processes, and crisis phenomena create uncertainty and lack of stability to entrepreneurship that results in the increase in risk of international business processes. Therefore, assessing the marketing performance of a domestic enterprise under the instability is of particular interest. This requires for quantitative and qualitative system-based and situational reasoning of its marketing development plan. The main objective of the paper is to determine the methodological approaches to assessing both the quantitative and qualitative results of an enterprise's marketing performance. It is determined that in the current context of the national economic system, the operation of business must include the actions directed to mutually agreed economic, image-building, informational, environmental, and social goals. In this regard, the concept of marketing strategy of an enterprise's functioning and development in a volatile environment based on the system-based and situational approach is developed, and the assessment tools to evaluate marketing strategy performance are proposed (marketing performance evaluation model based on sales revenue index; forecasting the amount of profit from participation in international business processes; plan of actions in cases of forecasting the profit from participation in international business processes taking into account the effectiveness of marketing strategies realization; PSR-FM method that allows to integrate evaluation results of customers' perceptual and transactional loyalty). The approaches to assessing the effectiveness of the enterprise's marketing strategy development allow to analyze both the marketing performance of an enterprise at large and the specific marketing initiative regardless of area of economic activity.