Herbivorous mammals benefit from foraging in family groups through the sharing of vigilance information and the dilution of the individual risks of being preyed upon; however, interference competition may reduce their intake rates. To evaluate the effects of family foraging on the individual foraging behavior of reed voles (Microtus fortis), the behavioral sequences and parameters of the voles' foraging on concentrated homogenous food patches consisting of fresh crabgrass leaves (Digitaria sanguinalis) were measured. The results showed that there is no significant difference in foraging behavior between female and male among family groups; however compared to a lone individual, individuals in family groups had significantly shortened foraging decision times, but markedly reduced intake rates. Analyses showed that, compared with the lone individual, the foraging interruption times of individuals increased significantly in family groups, but their intake rates declined significantly as a result of the greater amount of time spent on searching for adjacent food items. Analyses of the individual vigilance time showed that interference competition triggered by others individuals in family groups significantly increased the proportion of vigilance time spent on scanning, staring, and sniffing. While the proportion of vigilance time spent on upright scanning and listening decreased for individuals in family groups, the interruption times of individuals did not decrease significantly. These results revealed that the interference competition among individuals in family groups triggered variations in the parameters of the foraging behavior of the reed voles, increasing their foraging interruption times and decreasing their intake rates.