The effects of antimicrobial substances including nisin, acetic acid, lactic acid, potassium sorbate and chelators (disodium ethylenediamine tetraacetic acid [EDTA] and sodium hexametaphosphate [HMP]), alone or in combination and, with or without immobilization in calcium alginate gels, on the growth of Escherichia coli O157:H7 in ground beef were investigated. Results showed that acetic acid and potassium sorbate could inhibit the growth of E. coli O157:H7 effectively at 10 o C and at 30 o C. Both EDTA and HMP did not halt the growth of E. coli O157:H7. In an antimicrobial system immobilized with calcium alginate, most of the antimicrobials could not inhibit the growth of E. coli O157:H7 in ground beef at 10 o C and at 30 o C, with the exception of acetic acid and lactic acid. Immobilization did not enhance the effectiveness of acetic acid against E. coli O157:H7 in ground beef at 10 o C and at 30 o C (P>0.05) but it did enhance the effectiveness of lactic acid at 10 o C. In a system combining different antimicrobials, treatment with nisin /EDTA or nisin/potassium sorbate at 10 o C revealed a significantly lower population change of E. coli O157:H7 compared to samples treated with nisin, EDTA or potassium sorbate alone. The use of calcium alginate immobilization further enhanced the effectiveness of the combination system of nisin/EDTA, nisin/acetic acid and nisin/potassium sorbate on the growth of E. coli O157:H7 in ground beef at 10 o C but it was not effective at 30 o C.