The present study investigated NO3- and Br- contamination in groundwater of Arak aquifer of Markazi province. Correlation and factor analysis were used to detect interrelation and sources of concentration of NO3- and Br- ions and others physicochemical variables. No correlation was observed between NO3- and others contents, but positive correlation was identified between Br- with other major variables such as EC, TDS, Cl- and SO42- in the groundwater. The resulted data indicated that groundwater samples of two areas of Arak aquifer were severely contaminated with NO3- (up to 50 mg/L) and Br- (up to 0.5mg/L),which were exceeded the WHO and EU provisional guideline values. Nitrate was shown anthropogenic source and originated from sewage water from domestic and industrial activities. Bromide was originated from palaeo-salt water of Mighan Lake and has geogenic source.