A study of the effect of substrate concentration and temperature variation on batch anaerobic digestion of piggery waste was carried out in laboratory-scale completely mixed reactors. The variation of chemical oxygen demand (COD), total volatile fatty acids (TVFA), alkalinity, pH and methane production with digestion time followed the same pattern at mesophilic (35 degreesC) and ambient temperatures (16.8-29.5 degreesC). The process was more stable at mesophilic than at ambient temperatures. The rate of COD removal correlated with the digestion time through an equation of the Grau kinetic model type. An increase in the initial concentration of organic matter caused a reduction of COD removal rate. In addition, COD removal rates at ambient temperatures were significantly lower than those obtained at mesophilic temperature.