Although hematopoietic growth factors are at high levels in aplastic anemia (AA) patients, little is known about their dynamic change over time post treatment. We examined plasma concentrations of hematopoietic growth factors sequentially in 55 severe AA patients (45 treatment-naïve patients who had received immunosuppressive therapy (IST) or IST and eltrombopag; 10 IST-refractory patients who had received eltrombopag only), focusing on thrombopoietin (TPO). TPO concentrations were much higher than normal range in patients before treatment, then decreased in responders but not in non-responders. We followed up a cohort of 9 patients who obtained stable complete remission for up to 7 years post immunosuppressive therapy, and found that TPO levels declined gradually by 3 months post treatment accompanying an increase in platelet counts, but stabilized at the levels higher than normal range. An inverse correlation was noted between TPO levels and platelet counts. The increased plasma TPO levels could be required to maintain normal platelet counts in remission, as well as attributed to the reduced consumption by circulating platelets.