The study included 223 subjects divided into two main groups : First group (study group): - included 33 leukemic children whom infected with urinary tract infection. Second group (control groups): - consisting of three subgroups: (107 leukemic children, 48 urinary tract infection patients, 35 healthy children). Urine and blood specimens were taken, urine culture yielded 33 bacterial isolates from leukemic children whom were considered as bacteriological events Disinfection in studied patients, in addition to clinical suspicion, also other ICteriological isolates from UTI children was detected. Nineteen antibiotics were used in the antimicrobial susceptibility testing for c81 bacterial isolates, of these isolates 14(17.3%) were gram positive and 67(82%) were gram negative. The result of antibiotic susceptibility showed obvious resistance of bacterial isolates from leukemic UTI children as compared of bacterial isolates from UTI children particularly against chloramphenicol,cefriaxone,amoxycillin and norfloxacin", while sensitivity were showed to "amikacin, naldixic acid ,nitrofuration and ciprofloxacin. The most common bacterial type was gram negative bacteria particularly E.coli ,while gram positive bacteria come in the second after gram negative,Staphylococcus spp, formed the most common type of this group. sProtein concentration in urine was estimated for all groups by "Lowry method", and yielded increased protein concentration in urine specimen of leukemic children with urinary tract infection compared to urine specimen of leukemic children, but these increases statistically not significant at (p< 0.05). serum study included measurement of total serum protein by " Biurate methods"and yielded an obvious decline of total serum protein in leukemic children whom infected with urinary tract infection as compared with other leukemic children that not infected with UTI,and healthy children, but this decreases were not significant statistically (P<0.05). Another aspect of the study was to through insight on the immune response extended against urinary tract infection among the investigated groups of patients. Based on single radial immuno diffusion test (SRIDT), the result showed an obvious decreased of immunoglobulins " IgG, IgA, IgM" in leukemic children with urinary tract infection compared to specimen of other groups, but these increases statistically not significant at (p< 0.05). While complement component "C3 and C4" show obvious increase in leukemic children whom infected with urinary tract infection than other groups Furthermore, vero cell culture was used to study the adhesion and ; invasion of uropathogenic E. coil , which was isolated from leukemic children i with urinary tract infection.