Electrolyte abnormalities are common cause of morbidity and mortality in ICU patients. Quick and accurate results are required for immediate treatment. Conventionally these are measured in serum by electrolyte analyser but now point of care analysers are available to determine them in arterial blood by ABG. To measure electrolyte levels in venous and arterial samples and to evaluate the difference in them. The study was conducted in the department of biochemistry, GGS Medical College and Hospital, Faridkot. It was conducted on the total of 115 patients of either sex admitted in the intensive care unit (ICU). Arterial blood sample was collected for ABG and venous blood was processed in the electrolyte analyser. Results show that there is quite a difference between the mean values of these parameters in venous and arterial blood, with sodium having mean of 124.22 ± 9.18 in arterial blood and that of 137.09 ± 8.71 in venous blood. The mean value for potassium is 3.49 ± 1.28 in arterial blood and 4.21 ± 1.08 in venous blood. For chloride it is 108.54±9.9 in arterial blood and 101.77±7.2 in venous blood. The p values for all the parameters was <0.001. As we observed significant difference between electrolyte levels of venous blood done on electrolyte analyser and that of arterial blood done on ABG analyser so these cannot be used for in exchange for each other and so physicians should be cautious while reporting the results.