Henderson-Hasselbach equation (the basic calculation for Base Excess/BE and Anion Gap/AG), lactate concentration and Stewart modified equation (Base Defisit/Excess gap (BDE gap ) and Strong Ion Gap (SIG)) are the parameters frequently used by clinicians in order to determine the severity of metabolic acidosis in critically ill patients. The state of metabolic acidosis correlates significantly with poor outcome (mortality). Different methods were used to diagnose metabolic acidosis. The aim of this study was to analyze the correlation between acid-base balance parameters (BE, AG observed , AG calculated , SIG, BDE gap ) and lactate concentration with the outcome in critically ill patients with metabolic acidosis. This study is an analytic study with cross-sectional design involving 70 critically ill patients admitted ICU (Intensive Care Unit) of M. Djamil Central Hospital Padang. The study was conducted from January-September, 2016. Blood gas analysis was measured with potentiometric and amperometric method, electrolytes level was measured with ISE (Ion selective electrode) method and albumin level was measured with a colorimetric method (Bromocresol green/BCG). Multi variate analysis with logistic regression was used to determine which acid-base balance parameters strongly correlates with patient outcome based on odd ratio value more than 1 (OR>1). There were 33 male patients (47%) and 37 female patients (53%). Their ages varied in the range 18-81 years-old (SD 46.3±17.9) and mostly post operative (87%). The mortality rate reached the number of 33%. Logistic regression analysis showed the OR value for BE, AG observed , AG calculated , SIG, BDE gap and lactate were 0.859 (95% CI, 0.692-1.065), 0.628 (95% CI, 0.447-0.881), 1.470 (95% CI, 0.001-1.596), 0.892 (95% CI, 0.486-1.639), 1.785 (95% CI, 1.267-2.514) and 1.01 (95% CI, 0.10-1.96), respectively. All of the acid-base balance parameters and lactate concentration measured were correlated with the outcome of critically ill patients with metabolic acidosis and strong ion gap (SIG) is the best predictor of outcome in these patients.