This study was conducted to determine the effects of power ultrasound treatments on properties of Longissimus beef muscle. Twenty pairs of loins from steer carcasses, USDA Choice, maturity A were obtained 24hrs after slaughter for this study. Two experiments will be conducted at different intensity/time levels: (1) Control, 1.5 w/cm2, 3 w/cm2, and 5 w/cm2 for 3 minutes/side. (2) Control, 20 w/cm2, 40 w/cm2, and 60 w/cm2 for 45s/side (at 20 kHz) under refrigerated conditions. Each steak (four pieces) will be randomly allotted among these two experiments. Each loin was divided into at least 12 steaks and each steak was divided into 4 pieces, labeled, vacuum packed individually, and divided into groups: Day 1 and Day 7. Ultrasound treatments were applied using a direct probe commercial ultrasonic system. Cooking yields, shear force (Warner-Bratzler), and ultrasonic power entering the samples was measured. In addition, microscopy and SDS PAGE tests were conducted on the samples. No difference in shear force was observed for day 1, however at day seven the 5 w/cm2 treatment required a lower force (P < 0.05) to shear the sample. Histological cross-sectional samples for all treatments showed separation of the muscle bundles when compared with the control. SDS PAGE did not show any difference between treatments. Shear force values for day 1 were not significant, but showed a tendency toward lower shear values for the treated samples. At day 7, the shear force values were significant for the 40 w/cm2 treatment. The histological samples showed an evident separation of the muscle fibers. 5% gels indicated a possible degradation of titin at day 7.