Fatty acids are widely occurring in natural fats and dietary oils and they are known to have antibacterial and antifungal properties. This study assessed the inactivation activity of short- and medium-chain fatty acids against Ascaris suum eggs, which are routinely used as bio-indicators to the ovicidal activity of various manure and biosolids disinfection methods due to its inherent environmental indestructability and prevalence in sludges. Previous research has shown that the eggs could be easily killed when the pH of the acid solution was below the pKa of the acid, where most of the acid is in the undissociated form. Expanding on this earlier work, the acetic acid, butyric acid, valeric acid, and hexanoic acid alone or in combination with naturally occurring concentration at pH 4, were tested to determine the ability of eggs inactivation at 37°C. The inactivating factor was found to be a mixture of fatty acids. The results suggest butyric acid (240 mM) and hexanoic acid (16mM) at these low levels which are produced in a pilot toilet in development are capable of rapid inactivation of helminth eggs.