The present experiments were conducted to investigate the effect of protein (CP) and energy levels in concentrate supplementation on feed intake, ruminal ammonia nitrogen (NH3-N) and methylglyoxal (MG) production in swamp buffaloes (Bubalus bubalis) fed rice straw based diet. Eight Thai rumen fistulated male swamp buffaloes, about 4 years old with body weight (BW) of 381±10 kg, were randomly assigned to four dietary treatments in two consecutive 4 × 4 Latin square design experiments. Four buffaloes in first square received four different concentrate supplementations containing different CP levels at 92, 124, 181 and 219 g/kg while other four in the second square received different concentrate containing different total digestible nutrient (TDN) levels at 740, 761, 806 and 843 g/kg, respectively. All buffaloes were fed concentrate mixtures at 10 g/kg BW and rice straw was offered ad libitum. Under this investigation, the result revealed that total dry matter feed intake (DMI) increased with the increasing levels of CP (P<0.05) while increasing TDN up to 843 g/kg in concentrate mixture reduced DMI (P<0.05). Moreover, increasing CP and TDN levels in concentrate mixture reduced ruminal pH of buffaloes. However, ruminal temperature was not affected by either CP or TDN levels in concentrate mixture (P>0.05). In addition, ruminal NH3-N concentration and blood urea nitrogen of buffaloes increased with the increasing levels of CP in the concentrate (P<0.05) while there was no effect of TND level in concentrate on NH3-N and BUN of buffaloes in the second square (P>0.05). In addition, rumen MG productions were different among treatments by either CP or TDN levels in concentrate mixture, especially at 6 and 8 hour post morning feeding (P<0.05). The highest ruminal concentration of MG production was found in buffaloes received concentrate mixture containing CP and TDN levels at 124, 181 g/kg CP and 761, 806 g/kg TDN, respectively. The mean values of MG production concentration influenced by CP and TDN levels in concentrate mixtures were in the range of 24.5-28.1 and 3.8-4.5 mg/dl, respectively. Based on the present study, increasing CP and TDN levels in concentrate diet increased feed intake while ruminal pH was reduced. NH3-N and BUN concentration were increased by CP levels. Levels of CP and TDN between 124-181 g/kg CP and 761-806 g/kg TDN, respectively, in the concentrate mixture showed the highest ruminal MG concentration in swamp buffaloes fed on rice straw.