Presented are the results of hydrochemical work on the Amur river done during the freeze-up period in 2006, 2008 and 2011–2015 at the city of Khabarovsk and the villages of Leninskoe and Amurzet. The source of information used was represented by data of a joint Russian-Chinese monitoring of the water quality of the transboundary water bodies. We examine changes in the chemical composition of the Middle Amur water after transboundary pollution in November 2005 caused by the incident in the Jilin chemical plant (Songhua river basin). Emphasis is placed on the large role played by environmental measures in China (construction of pollution control facilities and hydraulic structures, shutdown of separate enterprises, etc.) in an improvement of the Songhua water quality. The influence of the regulation of the Zeya and Bureya rivers on the hydrochemical regime of the Middle Amur is shown. A characteristic is provided for the concentration distribution of dissolved matter along the length and width of the Amur in the section from Amurzet and Khabarovsk (400 km). The study revealed a smoothing of the differences in contents of the chemical composition components in the Amur waters along the width downstream of the inflow of Songhua. It is established that the Middle Amur water quality has improved in recent years: an increase in content of dissolved oxygen in the water, no pollution by nitrite nitrogen, and an abrupt decrease in ammonium nitrogen concentration. A predominance of the oxygenated form over the reduced form in the discharge was observed in the Middle Amur waters after 2012. A characteristic is given to the chemical composition of the Middle Amur waters during the freeze-up period after the historical flood of 2013.Keywords: Songhua river, hydropower construction, water quality, mineralization, bulk ions, biogenic substances.