A total of 17 samples of dairy products were collected from Baghdad markets. Nine isolates of Lactobacillus spp. were obtained, and identified as (4) Lactobacillus plantarum, (3) Lactobacillus fermentum, and one of each of Lactobacillus acidophilus and Lactobacillus brevis (1 isolate). Inhibition activity of Lactobacillus isolates against some pathogenic bacteria was tested on solid medium for different incubation periods. After that one isolate of Lb.plantarum was selected due to its highest inhibitory activity. The inhibitory effect of this isolate was also tested but in MRS broth at different incubation period. Results showed that 24 hr were the most efficient period of incubation for such purpose. Ability of the selected Lb.plantarum isolate to produce ?-galactosidase enzyme was detected in vitro by using X-gal as chromogenic substrate for ?-galactosidase which turn the color of colony from white to blue. To improve ability of the isolate in exhibiting inhibitory activity, various prebiotic substances (lactose, fresh whey and dried whey) with different concentrations (1, 2, 3, 4 and 5%) w/v (for lactose and dried whey) and (10, 20, 30, 40 and 50%)v/v (for fresh whey) were used, and three incubation periods (24, 48 and 72) hr were applied with defined inoculums size .Results testing inhibitory activity of Lb.plantarum with the above substances showed that Lb.plantarum propagated in MRS fortified with 2% lactose, 40% fresh whey and 3% dried whey with incubation period 48 hr (for each) had the best inhibitory activity compared to propagating, of Lb.plantarum in MRS alone. Minimum inhibitory concentrations ( MIC,s) of Lb.plantarum diluted concentrated filtrate were determined after propagated in MRS broth, and the same steps were repeated but when propagated in MRS broth containing the best three concentrations of prebiotics on Lb.plantarum activity. It was found that MIC,s value became lower after prebiotic treatment, with improving the activity against pathogenic bacteria. The ability of prebiotic substances for improving growth of probiotic, growth curve of the Lb.plantarum isolate propagated in MRS broth was determined then the growth curve was evaluated but when propagated in MRS broth fortified with the three prebiotics at concentration giving best effect on Lb.plantarum activity. It was found that growth of the probiotic bacteria was changed. Total viable count was performed for Lb.plantarum propagated in MRS broth with and without prebiotic after each incubation period (24, 48 and 72) hr. Results show that growth of probiotic bacteria was enhanced after the addition of prebiotic substances, this with concentrations of 2% lactose, 40% fresh whey and 3%dried whey.