In the Mekong Delta, husbandry household apply pig manure (PM) into anaerobic digester as waste treating which creates biogas for energy using. However due to rich nitrogen, anaerobic digestion of solely PM produces biogas in poor quantity and quality. This study investigated the effects of carbon-nitrogen (C/N) ratio on anaerobic co-digestion of PM and water hyacinth (WH) or rice straw (RS). The lab scale 21 L batch anaerobic apparatus were set up at WH or RS replacement to PM of 80+20, 60+40, 50+50 (mixing ratio counted base on organic dry matter of input materials). The results showed that biogas yield from PM+WH treatments of 80+20 (C/N 25.1), 60+40 (C/N 27.0), 50+50 (C/N 28.1) significantly higher than the treatment of 100%PM (C/N 23.5). For PM+RS treatment, the biogas yields of treatments 80+20 (C/N 26.2), 60+40 (C/N 29.8), 50+50 (C/N 32.1) significantly higher than the treatment of 100%PM. The CH₄ concentrated in biogas reaches the optimum values after 2 weeks that well suit for cooking purpose. It is strongly confirm that anaerobic co-digestion of PM with WH or RS is an effective way to achieve desired digestion performance.