This study examined the relationships among physicochemical properties and ultrasonographic image attributes of pectoralis major muscles in broiler chickens. Forty male Ross 308 chicks were randomly assigned to four equinumerous fat-supplementation groups (Group SO: soybean oil; Group FO: flax oil; Group SO + FO: soybean oil + flax oil; and Group BF: beef fat). Ultrasonograms of birds' pectoral muscles were obtained just before slaughter at 6 weeks of age and were subjected to digital image analyses to determine the mean pixel intensity (MPI) and pixel heterogeneity values (standard deviation of numerical pixel values; MPH). A total of 2, 4, 2, and 6 significant correlations were recorded in Groups SO, FO, SO + FO, and BF, respectively; there were no correlations with the chemical composition of the muscles in Groups SO and SO + FO. The strongest correlations were found between muscle lightness (L*) and MPH in Group BF (physical characteristic; r = -0.82, p = 0.003), and between crude fat/protein content and MPI/MPH of pectoral the major muscles in Groups FO/BF (chemical characteristics; r = 0.72, p = 0.02). There exists a potential application of ultrasonographic imaging and computerized image analysis for predicting certain physicochemical properties of pectoralis major muscles in broiler chickens.