Co-digestion between biomass and livestock waste increases methane production by providing an optimal C/N ratio. Also, bio-pretreatment has received more attention due to its effectiveness in biomass-derived material hydrolysis into biodegradable carbohydrates. Rice straw (RS) is abundant in the Vietnamese Mekong Delta (VMD), which potentially enhances biogas production from co-digestion with pig manure (PM) in case of shortage of livestock waste for biogas digesters. However, the high solid content of RS and its higher C/N ratio generally results in the low productivity of biogas when used as sole substrate. Therefore, we assessed the efficiency of biological pretreatment of RS on biogas production through single-stage batch anaerobic digestion under mesophilic conditions. The substrate ratio-based on volatile-solid (VS) rate was used at a 1:1 mixture (RS:PM) with a total concentration supplemented at 45 g-VS/L over a 60-day batch digestion. The bio-solutions included de-chlorinated tap water (TW), digester effluent (DE), ditch water (DW), and anoxic sediment (AS). The findings demonstrated that the pretreatment of RS enhanced biogas production by 78-84% compared with PM digestion without RS or bio-pretreatment. Likewise, AS and DE bio-solutions achieved the highest methane yield, which increased between 51% and 58%. Overall, the methane content (v/v) ranged from 50% to 55% during the stable phase, with VS removal efficiencies ranging from 39 to 46%. This study shows that DE and AS inoculums are feasible approaches for obtaining significant increases in biogas yields in co-digestion of RS and PM. Bio-solution pretreatment experimentation on distinctive biomass-derived materials under a series of C/N ratios is suggested.