Due to the lack of conclusive articles on the effect of guano, which is classified as a natural fertiliser, an experiment was conducted to evaluate its effect on the yield and quality of perennial ryegrass of the Rela variety. The guano used in the experiment contained significant concentrations in g·kg-1 DM of nitrogen (23.1), phosphorus (9.52) and magnesium (2.90). The concentration of heavy metals did not exceed the applicable standards in organic fertilisers. The total content of N and P in guano was higher relative to K, and Mg and Ca were similar. The concentration of N and Mg in guano is comparable to the content of these elements in poultry manure. The guano reaction was slightly acidic (5.86). The fertiliser value of guano was assessed in a vegetation-weed two-factor experiment. The test scheme included control, guano and guano with ammonium nitrate applied at three doses. The dry biomass yield of perennial ryegrass from individual cuts varied considerably. The objects with applied guano and guano with ammonium nitrate increased the average yield of perennial ryegrass from cut 1 by 102.9% compared to the control object. Applied guano fertilisation significantly increased the sum of perennial ryegrass yield from three cuts. As a result of the applied fertilisation, there was an increase in N, P and Ca content in perennial ryegrass, while K and Mg content increased to a negligible extent and thus contributed to optimal ionic ratios of Ca:P and K:(Ca+Mg). In contrast, the ionic ratio K:Mg deviated significantly from the optimal values for plants. The application of guano and guano with ammonium nitrate influenced the positive correlation between N and Ca content and the obtained yield of perennial ryegrass.