 Serial dilutions, as names suggest, is the series of sequential dilutions that are performed to convert dense solutions into more usable concentrations. In this video, we will learn how to quantify the bacterial concentration in a culture by using the Serial Dilution method. Objective of Serial Dilution is to estimate the concentration of organisms, it means bacteria, viruses of unknown sample. For example, if water sample is taken from highly polluted environment, then dilution factor must be increased. If we take water sample from less concentrated solutions, then low dilution factor might be sufficient. For the preparation of Serial Dilutions, falling procedure is used. For procedure, first take 6 test tubes having 9 NML, 6 sterile distilled water. The micropiped at 1000 microlitre for taking the sample, 1 ml sample first test tube. Mix the sample properly in first test tube after mixing, take 1 ml sample again from first test tube to second test tube having 9 ml sterile distilled water. Again mix the sample properly from second test tube, take 1 ml and transfer it to third test tube. The same procedure could be used for all 6 test tubes, 6 test tubes to last 6 test tubes and properly mix the solution. After addition of solutions, label each test tube with dilution factor. This test tube is 10 raised to minus 1 dilution, second 10 raised to minus 2, third 10 raised to minus 3 and so on. After completion of preparation of Serial Dilutions, we use these Serial Dilutions for inoculation on a specific media. Basically the purpose of Serial Dilution is by simply taking sample from one test tube and then dilute it with the help of sterile diluent which may be distilled water or may be 0.9 percent saline solution.