Introduction: Analysis of urine from dogs and cats are an important method for diagnosingkidney and urinary tract diseases. Earlier studies have suggested that urine needs to be acidifiedbefore analysis of calcium and phosphorus to obtain a more reliable result. The acidification ismeant to dissolve urinary crystals which could affect the analysis. Aim: The aim of this study was to investigate if acidification of dog and cat urinary samples isnecessary for reliable analysis of calcium and phosphorus. The study also aimed to investigate ifacidification is possible after the freezing of urine, and also evaluate the stability of acidifiedurine and supernatant in -80 °C freezer. Material and method: Forty-four urinary samples, of which 38 were from dogs and 6 from cats,were collected. Each sample was divided into three aliquots; one aliquot was acidified directly,one aliquot was acidified after storage in the freezer, and the last aliquot was centrifuged and thesupernatant was collected. Calcium and phosphorus were analyzed with an automatic chemistryinstrument in all aliquots before and after storage in -80 °C. The presence of urinary crystals wasinvestigated through a microscope. Results and conclusion: The calcium and phosphorus concentration were not higher in acidifiedurine, so acidification does not seem to be required for analysis of calcium and phosphorus indog and cat urine. Acidification after storage of urine in the freezer gave similar results asacidification of fresh urine. Both supernatant and acidified urine were stable in -80 °C for at least 3 days.