To observe the effect of extract of Carapax et Plastrum Testudinis (ECPT) on nuclear receptor in the proliferation of rat mesenchymal stem cell (MSC) in vitro. The rat MSC dissociated from bone marrow by density gradient method were cultured and identified by marking of bromodeoxyuridine (Brdu) and staining of CD44. Then different doses of ECPT (3333, 333.3 and 33.33 μg/mL) were respectively added into in-vitro cultured MSC for 12, 24, 72 and 120 hours. The expression of retinoic acid receptor-α(RARα), vitamin D receptor (VDR), estrogen receptor (ER), glucocorticoid receptor (GR), thyroid hormone receptor-α(TRα) and peroxisome proliferator-activated receptor δ(PPARδ) in MSC was detected by immunohistochemistry and immunofluorescence methods. The number of RARα-and VDR-positive cells in ECPT groups was higher than that in the control group (P < 0.05 or P < 0.01) and the effect was in a dose-dependant manner. RARα expression in MSC arrived at the peak after 24-hour culture with ECPT, and VDR expression arrived at the peak after 72-hour culture. ER-, GR-, PPARδ- and TRα-positive cells were undetectable in ECPT groups. RARα and VDR probably are the pharmacological targets in ECPT promoting the proliferation of MSC.