Red mud, a waste tailing from alumina production, was activated with calcination and acid treatment for simultaneous removal of F- and As from water solution. After activation, the specific area and Si-O-M and Al-O-H functional groups of the activated red mud (ARM) greatly increased. Results showed that the adsorption equilibrium time for F-, As(V), and As(III) was 18, 12, and 48 h, respectively. Kinetic data revealed that adsorption kinetics well followed the pseudo-second order model for F-, As(V), and As(III). The presence of As(V)/As(III) improved the adsorption rate of F-. With the co-existence of F- and As, F- adsorption was independent of initial solution pH between 4.0 and 10.0, and As adsorption between 2.0 and 10.0. Adsorption of F-, As(V), and As(III) was better described by the Langmuir model than the Freundlich model, indicating that adsorption was in the form of a monolayer. Fluoride had a significant effect on As(V) adsorption, while the less affected As(III) adsorption. The presence of 1.0 mg/L As(III)/As(V) had no significant influence on F- adsorption. ARM had high adsorption capacity for F-, As(V), and As(III), which resulted from the increases in the specific area and Si-O-M and Al-O-H functional groups. Results demonstrated that ARM is a potential adsorbent for simultaneous removal of F- and As from contaminated groundwater.