Twenty-eight day-old piglets were inoculated with classical swine fever virus (CSFV) attenuated C strain propagated in ST cells at different doses (106 TCID50 and 105 TCID50). The immuno-efficacy was evaluated by clinical symptoms, pathologic autopsy and histopathology, antibody detection, lymphocyte proliferation assay and antigen detection. The results showed that this C strain induced no observed clinical symptom, no viremia, no virus shedding. An identical booster immunization was conducted 3 weeks post primary immunization，about 10 days after the second immunization, the CSFV specific antibody changed to be positive and the level of which arrived at a peak 20 days after the second immunization. In conclusion, the CSFV C strain propagated in ST cells is safe and efficiency to the piglets.