Objective　To analyze the percentage and functional changes of natural killer T (NKT) cells in peripheral blood and bone marrow of severe aplastic anemia (SAA) children before immunosuppressive therapy (IST) comparing to that of healthy children. Methods　Ten children with severe aplastic anemia were included in the study and ten healthy children at the same age were selected as the control group. By flow cytometry, the percentage of CD3+CD1d tetramer+ NKT cell in peripheral blood and bone marrow were detected from March 2014 to December 2014 in our hospital. Immune magnetic bead separation was used to isolate and purify iNKT cells .The purified iNKT cells were cultured in the OCH(50 ng/ml, 100 ng/ml or 200 ng/ml) ＋ rhIL-2 ＋ rhG-CSF culture systems. The amplification of iNKT cells after cultured in different systems were calculated. Elispot method was used to analyze the spotting form cells (SFCs) of IFN-γ or IL-4 expressed by activated iNKT cells. Results　The percentage of CD3+CD1d tetramer+ NKT cells in peripheral blood of SAA group (0.72±0.03)% was significantly lower than that of the control group (0.92±0.02)% (P=0.000). The percentage of CD3+CD1d tetramer+ NKT cells in bone marrow of SAA group (0.82±0.02)% was significantly lower than that of the control group(1.05±0.05)% (P=0.000). In vitro iNKT cell amplification ability of bone marrow in SAA group was significantly lower than the control group, and in medium concentration (50±6) and high concentration OCH group (52±6), the amplification ability was higher than that in low concentration OCH group (30±5) (P<0.05). The secretion of IFN-γ in the iNKT cells of SAA bone marrow was significantly lower in medium concentration (33±3) and high concentration (35±3) OCH group than that of the low concentration (50±3) OCH group (P<0.01). The secretion of IL-4 in the iNKT cells of SAA bone marrow was significantly higher in medium concentration (50±3) and high concentration (75±3) OCH group than that of the low concentration (33±3) OCH group (P<0.01). Conclusions　The quantity and function of NKT cells from children with SAA are lower than that of the healthy children. In vitro, they had better amplification ability and could improve IL-4/IFN-γ imbalance in medium concentration and high concentration OCH group than in low concentration OCH group.