Vehicles produced harmful gases such as Carbon Monoxide (CO) and Hydrocarbon (HC) and this gas emission continue to increase every year. In 2018, there was an increase of up to 10% from the previous year. This gas is harmful to human and the environment. One way to reduce pollution from vehicle emissions is by adsorption. Adsorption is often used because its large adsorption capacity reaches 95%. Of the several types of adsorbents, the most developed ones are activated carbon because of its low price and high adsorption ability. The use of commercial activated carbon has begun to be replaced with activated carbon made from biomass waste because it is cheaper and environmentally friendly. CO and HC gas molecules can be absorbed properly in activated carbon. To improve the adsorption ability of activated carbon, it is modified with Magnesium oxide (MgO) with impregnation method. With modifications using activated carbon and MgO ratio of 70:30, 80:20, and 90:10, the surface area results are 1149.48 m2/g, 890.23 m2/g, and 859.91 m2/g. CO and HC Adsorption were carried out with inside tube variant of 3 cm, 4 cm, and 5 cm. this inside tube is used to put the adsorbent. The results showed with increasing the length of the inside tube, the CO adsorption yield increased from 78.68 to 99.14% and HC to 64.54 87.73%. So the modification of AC with MgO had a significant effect for pollutant gases adsorption.