The present study was conducted to investigate biogas production from unused biomass at households in My Thuan hamlet, My Khanh commune, Phong Dien district, Can Tho City, Vietnam located in the Mekong Delta. We employed four treatments: pig manure (the control treatment), water cabbage (Pistia stratiotes), water hyacinth (Eichhornia crassipes), and orchard grasses in triplicate, with each replicate lasting 60 days. Our results showed that the average amount of biogas did not differ significantly between the four treatments, with values of 7,201 ± 641 L for pig manure, 6,445 ± 1,783 L for water cabbage, 5,170 ± 2,664 L for water hyacinth, and 6,924 ± 2,688 L for orchard grasses. The concentrations of CH₄ in pig manure, water cabbage, water hyacinth, and orchard grasses were 55.7%, 55.1%, 52.0%, and 47.4%, respectively. The average CH₄ concentration did not differ significantly between treatments. Therefore, water cabbage, water hyacinth, and orchard grasses can replace pig manure in biogas production.