Sir, Fish liver oil is recognized as the main source of Vitamin D3 in the human diet. It has yet to find a place in the Iranian dietary pattern; however, its frequent consumption is due to medicinal prescription and as a dietary supplement. Fish oil and fish liver oil have also been recognized in some recent Iranian intervention trials as a beneficial Vitamin D3-containing ingredient.[1,2,3,4,5,6,7,8,9,10] Based on the results of international studies, the concentration of Vitamin D3 and its derivatives in fish liver oil falls within the range of 40-200 IU/ml.[11] Moreover, in “Krause's Food and the Nutrition Care Process,” one of the most used textbook by nutritionist, the concentration of Vitamin D3 in fish liver oil is reported as 1060 IU per tablespoon that is equal to 70.6 IU/ml.[12] Overviewing the Iranian scientific literature in this filed reveals that only one study was conducted on the determination of Vitamin D3 concentration in fish and fish liver oil. In this work, comparing different Vitamin D3 extraction methods, the authors reported on the Vitamin D3 concentration of Caracharhinus machoti liver oil as 0.02746 mg/ml, corresponding to 1098 IU/ml of extracted oil, and Vitamin D3 concentration in 100 g of Clupeomolla grimi flesh as 0.1028 mg that is equivalent to 4115 IU.[13] In the current available nutritional table used by Iranian nutritionists, which is a translated version from English, Vitamin D3 concentration in fish liver oil is stated to be 210 μg that is equal to 8400 IU/100 g oil.[14] Considering specific weight of oil as 0.9 g/cm3, each milliliter of fish liver oil contains 70.6 IU Vitamin D3 that is exactly the value which is presented by krouse, whereas the value mentioned in Iranian study is approximately 15 times larger than this amount. Moreover, regarding the oil extracted from fish body, the data presented in the given nutritional table for Vitamin D3 concentration of 100 g of fish types similar to Clupeomolla grimi are mentioned as 13-19 μg identical to 520-760 IU[14] that is 5-8 times less than that of measured in the Iranian study. Comparing the above-mentioned data indicates a noticeable disagreement in the Vitamin D3 content of fish and fish oil between Iranian and international scientific sources. Since the higher sunshine intake, the higher Vitamin D3 accumulates in the sea animal's body[15] such differences might be due to geographical difference between the origins of tested samples in the above-mentioned studies. As in evaluation of the nutritive value of food articles, Iranian nutritionist used to use the nutritional tables from scientific resources other than the native ones, such differences could be regarded as source of error when the homemade fish oil products are used as a supplement of Vitamin D3 in the recommended diets; however, to clearly address the issue, more study should be conducted on the presence and concentration of Vitamin D3 in the fish oil and fish liver oil prepared in the country. Since, in order to estimate the nutritive value of food articles, Iranian nutritionist used to use the nutritional tables from scientific resources other than the native ones, such a difference could impress a source of error when the homemade fish oil products used as a supplement of Vitamin D3 in the recommended diets. However, to clearly adders the issue, more study should be performed on the presence and concentration of Vitamin D3 in the fish oil and fish liver oil prepared and used in the country.