Water hyacinth (WH) biomass is one of the popular materials in the Vietnamese Mekong Delta, a potential substrate for biogas production. The effectiveness of utilizing WH for producing biogas under anaerobic digestion was demonstrated in the previous studies, but the research was focused on the loading rate of about 1.0% volatile solid (VS). Therefore, in the present study, a semi-continuous anaerobic digestion experiment was conducted with the five levels of VS, including 1.0%VS, 1.5%VS, 2.0%VS, 2.5%VS, and 3.0%VS, to examine how loaded VS can affect biogas production. Each treatment was designed with three replications over 60 days. The measured parameters included pH, temperature (Temp; °C), redox potential (Eh; mV), daily produced biogas volume (L), cumulative biogas volume (L), and methane (CH4 ) concentration (%) during the 60 days of the experiment. The obtained results showed that pH, tempt, and Eh parameters did not negatively affect biogas production. However, the volume of daily biogas in the treatment of 3.0%VS was higher than in other treatments. In addition, the cumulative biogas volume in the treatment of 3.0%VS was the highest and significantly different between all reactors (p