Humic substances (HS) are amorphous organic macromolecules that are responsible for the color of natural water and wastewater effluents. They play an important role in the formation of disinfection by-products. The ultrasonic process is applied as a treatment method to investigate its effect on the TOC removal and the formation of trihalomethanes (THMs) during chlorination. It was observed that the metal ions such as Fe(II) and Mn(II) showed catalytic effects while AI(III), Ca(II), and Mg(II) had inhibitory effects on the TOC removal of humic substances in sonochemical reaction with hydrogen peroxide. Experimental results also showed hydrogen peroxide dose affected the formation of disinfection by-products. Chloroform and dichlorobromomethane were formed as major THMs during chlorination.