The immunomodulatory properties of ethanolic leave extract from Tridax procumbens was investigated in Swiss albino rat orogastrically dosed with Pseudomonas aeruginosa. The animals were divided into six groups of four per group. The first group was given the standard inoculum of Pseoudomonas aeruginosa only and the second group was given 8 mL of the standard inoculum of the organism and treated with ethanolic extract of Tridax procumbens. The third category was given the ethanolic extract of Tridax procumbens only while the last group was given normal saline. The uninfected rats showed a (WBC) values of 4,080 mm3 which increased to 8,400 mm3 during infection and later dropped to 3,700 mm3 after infections was treated with the extract from Tridax procubens. The PCV was normal before infection, dropped during infection and increased after infection was treated with extract. The rats infected and treated with Tridax procumben showed a WBC, PCV, neutrophil lymphocyte and eosinophil count of 4,100 mm3, 53, 46, 53 and 1%, before infection; a count of 4,600 mm3, 29, 50, 50 and 0%, during infection and 3,400 mm3, 42, 62 and 32%, respectively after infection. The rats given extract only showed a WBC, PCV, neutrophil, lymphocyte and eopsinophil counts of 5, 840 mm3, 53, 51, 48 and 1%, before infection; a count of 5,400 mm3, 31, 49 and 51% during infection and 4,000 mm3, 36, 68 and 30%, respectively after infection. The control rat showed little or no increase in WBC, PCV, neutrophil, lymphocyte and eosinophil count. The urinalysis showed that the rats had pH of 6, Negative to glucose, ketone, nitrite, ascorbic acid, protein, bilirubin, blood and normal urobilinogen for all groups before infection. The control rats showed a pH of 6, negative to glucose, ascorbic acid, ketone, nitrite, protein, bilirubin, blood and normal urobilinogen which showed the same pattern with all groups before infection. The urine microscopy revealed large number of pus cells, casts, crystal and bacterial cells during infection in those infected with the Pseudomonas aeruginosa only. While infected - treated rats showed a reduced number of pus cells, casts, crystals and bacterial cells during infection. These results showed that ethanolic extract of Tridax procumbens has immunomodulatory properties and it is able to inhibit proliferation of Pseudomonas aeruginosa.