Water quality is one of the main issues all over the World and its improvement is a major concern. The importance of nutrients (compounds of N, P, Si, Fe) in surface waters is determined by the fact that in natural concentrations these substances serve as the main food source for aquatic organisms, but in large concentrations, caused by pollution processes, they become sources of eutrophication and degradation of aquatic ecosystems. The current study was based on the monitoring of nitrogen compounds in the Lower Prut (sector Gotesti - Giurgiulesti) during the vegetation period of 2014 – from March to October. The chemical analyses were performed by using spectrophotometric methods and applying a range of national and ISO standards. Altogether, the concentration of ammonium ions ranged from 0.002 mg N/l (May, Gotesti, Giurgiulesti) to 0.291 mg N/l (March, Cahul). In spring the highest concentrations of ammonium ions were registered in Gotesti - Cahul, and in autumn – in Slobozia Mare– Giurgiulesti sectors. In average the lowest concentrations of ammonium nitrogen were recorded in May, reaching a maximum of 0.06 mg N/l at Slobozia Mare station, and, opposite the highest concentrations were found at the end of summer-beginning of autumn. The high figure from March can be the result of the process of complete decomposing of organic compounds in winter period, and also of surface run-off from adjacent territories. There was a slight increase of nitrite nitrogen (N-NO2 -) content along the river, higher values being recorded at Slobozia Mare and Giurgiulesti stations (in March- 0.03 mg N/l for both stations, in May- 0.024 mg N/l at Giurgiulesti, in July- 0.015 mg N/l at Giurgiulesti and in September and October - 0.02 mg N/l, also at both station). The increase of nitrite nitrogen content in spring period pointed out a recent pollution of aquatic ecosystem, this fact coming across to hydrochemical regularities – as rule, the content of nitrites is the highest at the end of summer-beginning of autumn. If optimal oxygenation conditions exist, the nitrogen is found mainly in the form of nitrates (N-NO3) - the most accessible form of nitrogen for plants and microorganisms. In particular, the highest values of nitrate nitrogen were found during spring floods, with an average value of 1.629 mgN/l and the lowest – during water low level in autumn, correspondingly 0.778 mgN/l. In general, the share of ammonium ions in the content of mineral nitrogen ranged 10-20%, of nitrite ions – 2-6% and of nitrate ions - 75-90%. It is worth to mention that the content of mineral nitrogen decreased along the river. In most of months the content of mineral nitrogen exceeded that of organic nitrogen, for example, in July it formed from 55% (Cahul) to 90% (Gotesti) of total nitrogen, in September – more that 85% at all sampling stations. Only in May and October the ratio between mineral and organic nitrogen was almost 1:1. During vegetation period of 2014 the values of total nitrogen was higher in May and, as a whole, an increase along the river from 0.263 mg N/l (upstream Gotesti) to 3.544 mg N/l (Slobozia Mare) was recorded. In accordance with enforce regulations of the Republic of Moldova (Regulation on environment quality requirements for the surface waters, 2013), the registered concentrations of three indicators based on nitrogen compounds, namely ammonium nitrogen, nitrate nitrogen, and total nitrogen (including organic), indicated the classes of water quality I – II (very good – good), and of the forth one - nitrite nitrogen – the class II (good).