The anti-bacterial efficacy of medium-density polyethylene (MDPE) with various contents of different anti-bacterial agents was studied with respect to the effects of the anti-bacterial concentration, size and form of MDPE test-specimen, and the contact time. The three anti-bacterial agents used were carbendazim and zinc dimethyl dithiocarbamate (TROYSAN-S88), 2-hydroxypropyl3-piperazinyl-quinoline carboxylic acid methacrylate (HPQM), and silver substituted zeolite (ZEOMIC). The halo and plate-count-agar (PCA) tests were employed to assess the efficacies of the anti-bacterial performance. It was found that the inhibition zone from the halo test was most visible for the HPQM agent; the higher the HPQM content, the greater the inhibition zone. ZEOMIC exhibited no inhibition zone. The PCA test results suggested that after incorporating HPQM agent in the MDPE matrix, the% reductions of E. coli and S. aureus bacteria were as successfully high as 99.9% for all HPQM loadings.