Anaerobic digestion technology (biogas) has been introduced to treat for husbandry wastes in the Mekong Delta of Vietnam for more than 30 years. However, biogas application is limited. One major barrier is lack of input material to biogas digester as husbandry is normally processed at households scale. Meanwhile, rice straw is available in huge quantity in the Mekong Delta, but it is seldom put in use. This study focuses on testing the suitability and efficiency of anaerobic co-digestion of rice straw and pig manure to produce biogas. The study used 21 L lab-scale batch anaerobic co-digestion pig manure and rice straw in different sizes of straw. The mixing ratio for co-digestion was 50% : 50% based on organic dry matter values of input materials. The result showed that control parameters of temperature, pH, alkalinity and redox potential of almost treatments were in suitable range for activities of methanogenic micro-organisms. The biogas yield of the treatments with straw size of 1.0 cm was 691.05 L/kg ODM_fermented, of 10.0 cm - 687.79 L/kg ODM_fermented, of 20.0 cm - 685.08 L/kg ODM_fermented and of original size - 680.44 L/kg ODM_fermented, which was not significantly different to that of the treatments of 100% pig manure. The CH₄ content tended to increase by time since the 2^nd week and is well qualified for energy using purpose. The result strongly confirmed that rice straw could be applied as an additional material to pig manure to produce biogas, and chopping rice straw is unnecessary.