A new cationic dimeric surfactant (DS) has been synthesized using fatty acids separated from neem oil. The dimeric surfactant synthesized from neem oil-based fatty acid holds antibacterial property like the neem oil. A well plate method was used for the assay. Prepared dimeric surfactant was characterized by FTIR and 1H NMR, while fatty acids were characterized by GC, acid value, and SAP value. The most effective CMC (critical micellar concentration) value and surface properties of the dimeric surfactant were characterized by the pyrene probe method as well as the Wilhelmy method. Surface tension (SFT) and interfacial tension (IFT) value helps to know the wide application of the compound. Dimeric surfactant generally shows lower surface tension as compared to monomeric surfactants. Neem fatty acid-based dimeric surfactant shows 28 mN/m surface tension. Lamella strength is also good for the compound whereas interfacial tension was 3 mN/m. Such an effective surfactant was also used in nanoemulsion and particle size was determined, and it gives stable emulsion from the emulsification index. Dimeric surfactant prepared from neem fatty acid shows very good wettability and foaming property.