The aim of this study was to determine the effects of glyphosatę ammonium salt on the activity of some enzymes involved in the metabolism of phosphorus in the soil: acid phosphomonoeaterase (EC 3.1.3.2), alkaline phosphomonoeaterase (EC 3.1.3.1), phosphotrieaterase (EC 3.1.5.1), inorganic pyrophosphatase (EC 3.1.6.1), and a phosphorus content in a form available to plants. The experiment was carried out on loamy sand samples with organic carbon content 8.7 g kg^-1. Into soil samples the aqueous solutions of Avans Premium 360 SC (360 g glyphosate ammonium salt in 1 dm³) were added. The amount of introduced glyphosate ammonium salt was 0 (control), 1, 10, 50 and 100 mg·kg^-1, on days 0 (1 hour after glyphosate application), 7, 14, 28 and 56 measured parameters were determined spectrophotometrically. The obtained results showed that the application of glyphosate ammonium salt resulted in changes of available phosphorus content and the activity of enzymes involved in the metabolism of this element in loamy sand. The effects glyphosate ammonium salt dosage and effect of day of experiment were ambiguous. Among the determined parameters the most sensitive to the presence of the glyphosate ammonium was alkaline phosphomonoesterase.