Guinea pigs are common patients in veterinary clinics. Knowledge of the urine composition is necessary for the evaluation of their health. We, therefore, analysed the urine of fifty guinea pigs, thirty-two males, and eighteen females, aged between four months and seven years. None of these guinea pigs showed clinical signs of urinary tract diseases. The urine samples were obtained as part of a preventive check-up, during a regular dental check-up or another minor procedure. The urine was acquired by spontaneous micturition after inducing a short-term, light isoflurane anaesthesia. A macroscopic evaluation of the urine samples and a urine dipstick test were used for the preliminary examination. The average pH was determined to be 8.5 ± 0.5, and in three animals, moderate glycosuria was detected using the urine dipsticks. No urobilinogen, ketone bodies, haemoglobin, or blood traces were present in any of the samples. Severe proteinuria was detected in all the samples. The samples were subsequently evaluated in a laboratory for the following values: specific gravity 1 024.40 ± 1.83 kg/m³, osmolality 601.14 ± 52.28 mOsm/kg, total protein 290.16 ± 34.73 mg/l, albumin 12.04 ± 1.92 mg/l, glucose 0.77 ± 0.20 mmol/l, urea 217.60 ± 24.23 mmol/l, creatinine 3.98 ± 0.48 mmol/l, bilirubin 9.63 ± 1.73 μmol/l, calcium 6.14 ± 0.40 mmol/l, phosphorus 4.95 ± 1.30 mmol/l, magnesium 9.86 ± 0.57 mmol/l, sodium 49.15 ± 6.67 mmol/l, potassium 152.21 ± 10.62 mmol/l, chloride 51.14 ± 5.81 mmol/l, activity of gamma-glutamyltransferase 0.72 ± 0.14 μkat/l, alkaline phosphatase 0.56 ± 0.11 μkat/l and lactate dehydrogenase 0.68 ± 0.14 μkat/l. The descriptive values of the urine biochemical parameters of guinea pigs were determined for the first time in this study.