Abstract: Objective To investigate sub-acute toxicity of recombinant human lactoferrin(rhLf) from cattle mammary bioreactor in mice.Methods Groups of 12 male and 12 female weaning Kuming mice were fed with AIN-93 purified diets for laboratory rodents(control group) or rhLf modified diets(treated group),in which 20 g casein/100 g AIN-93 diet was substituted for 20 g rhLf/100 g diet,for a consecutive 28-day period.Body weight and food intake were recorded weekly.At the end of the study,blood was collected for routine and biochemical blood examination and organs were dissected and weighted;histopathological examination was accomplished simutaneously.Results The final mean body weight of rhLf-treated male mice was 38.3 g?3.1 g,higher than that of the control (34.9 g?4.3 g) significantly,but there was no significant difference between two female groups(31.2 g?2.4 g in the treated and 31.2 g?1.9 g in the control).Food utilization rate,routine blood examination and biochemistry,absolute and relative weight of organs,and histopathology of organs of treated male and female mice were similar to those of the controls.Conclusion No evidence of sub toxicity was observed in the mice administered with recombinant human lactoferrin for 28 days.