This part of the study was also carried out at the laboratories of both Hort. Res. Inst., ARC, Giza and Agric. & Biol. Res. Div., NRC, Dokki on about 31 ornamental plant species belong to 12 families chosen from different places inside the field of Japanese garden, that lies at Helwan industrial City, Cairo, Egypt during the summer season 2017 in order to compare the tolerance degree of these various species against the air pollution prevailing in this city, beside testing the effect of their planting place on their tolerance. Thus, leaf samples from the selected plants were monthly collected in the early morning for 3 times and analyzed to evaluate 4 physio-biochemical characters involving: ascorbic acid content, relative water content (RWC), leaf extract pH  and total chlorophyll content, which were used afterwards to calculate the values of air pollution tolerance index (APTI). The APTI scale was also used for determination of tolerance degree (level) for every plant species. The results have shown that means of ascorbic acid content, RWC, leaf extract pH, total chlorophyll content and APTI values were markedly differed with various significance levels due to variation of plant species and planting place. So, each species (under each family) exhibited a different tolerance degree against air pollution than the other species of its family. Such tolerance degree was also changed with changing of planting place inside the area of the garden. Accordingly, at least it can be recommend to choose the following ornamental species (from each family) for tolerance against the air pollution at Helwan city: Schinus molle (Anacardiaceae), Plumeria alba (Apocynaceae), Cycas revoluta (Cycadaceae), Cassia fistula, C. nodosa and delonix regia (Leguminosae), Yucca elephantipes (Liliaceae), Hibiscus rosa-sinensis (Malvaceae), Ficus benghalensis (Moraceae), Washingtonia filifera (Palmaceae), Pinus halepensis (Pinaceae) and Lantana camara (Verbenaceae).