Aromatic properties of two series of quinoline derivatives were studied theoretically using the Density Functional Theory (DFT) approach. One series of compounds possesses antimalarial activity while the other does not have such properties. The B3LYP functional and the 6-311++G** basis set were employed in the study. The optimized geometries of the studied compounds were used for aromaticity level determination using several aromaticity indices, like HOMA, NICS, PDI, I6, FLU, and PLR. It was shown that the level of aromaticity seems to be a feature that differentiates these two series of compounds. This is reasonable because it has been presented, previously in the literature, that this type of drug acts as an antimalarial drug through the formation of the π-π complex with ferriprotoporphyrin. There are two types of rings in the quinoline system, a benzene type, and a pyridine type. The aromaticity of the benzene-type ring in both series of studied compounds is similar while the aromaticity of the pyridine-type ring is lower for compounds that have antimalarial properties. It is derived on the basis of performed research that the properties of the pyridine-type ring are more important for the drug activity of studied compounds.