Methanesulfonic acid (MSA) was used as the catalyst to remove trace olefins from aromatics (referred to as oil). The reactions were conducted in a round-bottom flask equipped with a reflux condenser and oil-bath under atmospheric pressure. The influences of the reaction temperature, the mass ratio of MSA to oil, and the reaction time were investigated. The experimental results showed that after a 40 min reaction time at 413 K, the olefins conversion of 89.45% was obtained with a mass ratio of MSA to oil of 6%. The catalyst was reused five times without a reactivation treatment, and the olefins conversion reached 66.02% the fifth time. More importantly, the catalytic mechanism was also proposed in this work. In addition, as MSA is biodegradable, this method represents an environmentally benign route to remove trace olefins from aromatics.