This research mainly studies the effect of potato peel phenolic compound on cow butter as a preserving agent. It was extracted from potato peel (solanium tuberosom species) waste which delays spoilage and oxidation of most oil and lipid containing foods. It inhibits these foods from microbial spoilage and oxidation reaction formation causing undesirable and toxic product formation. This phenolic compound is extracted from the peel by the method of maceration extraction with ethanol solvent. The percentage yield obtained was 10.42 ± 0.03% and the presence of major phytochemicals (phenol, flavonoid and tannin) were checked. The total phenolic compound was determined by Folin–Ciocalteau methodology with uv-spectrophotometr and the total flavonoid content was determined by the method of aluminum chloride colorimetric method. From this, a total phenolic content of 2.9468± 0.03 mg GAE/g of dry extract and a total flavonoid content of 3.6885±0.02 mg Quercetin equivalent /g of dry extract were obtained. The potato peel extract was then applied on cow butter with different concentrations (0.2%, 0.3% and control) and two storage temperatures (20oC and 45oC) for a total storage time of 21 days. So that the microbiological (aerobic total bacterial count and yeast-mould count) and chemical parameters (peroxide value and free fatty acid value) were analyzed. The result indicated that from the two storage temperatures storing a butter sample at 20oC and an extract concentration of 0.3% showed better preservation for aerobic total bacterial count, peroxide value and free fatty acid value than other treatments done here. For yeast-mould count storing butter sample at a temperature of 45oC and 0.3% extract concentration shows lower number than the rest treatment. But storing the butter sample at high temperature (45oC) without extract caused high number of bacteria and high formation of peroxide value and free fatty acid value.