Nitrogen oxide (NOx) is one of the polluting gases harmful to humans and the environment. Nitrous oxide gas is mostly found in air, namely nitrogen monoxide (NO) and nitrogen dioxide (NO2). NOx gas in the air, which mostly comes from exhaust gases, needs to be reduced to minimize the hazards to humans and the environment and comply with applicable regulations regarding hazards. The absorption process with a membrane contactor is an alternative to reduce NOx concentrations in the air. This study evaluates the hollow fiber membrane modules' performance in the NOx absorption process using sodium chlorate (NaClO3) and sodium hydroxide (NaOH) as an absorbent solution. Based on the experimental results, the NOx reduction efficiency increased with an increase in the absorbent concentration and the amount of fibers in the membrane module but declined with an increase in the feed gas flow rate. The highest value of NOx reduction efficiency, the overall mass transfer coefficient, the flux, and the NOx loading obtained in the study were 99.7%, 0.01743 cm s -1 , 9.510 x 10 -8 mmole cm -2 s -1 , and 0.026 mole NOx/mole NaClO3, respectively.