AbstractThe aim of this study is to determine the cut‐off value of glucose‐6‐phosphate dehydrogenase (G6PD) activity and the mutation spectrum of G6PD gene in neonates with G6PD deficiency at Ningbo. Around 82233 neonatal blood samples were measured to determine G6PD activity. The positive samples were further detected with gene analysis. A total of 445 neonates were confirmed as G6PD deficiency, and the incidence in Ningbo was 1/185. 17 types of G6PD gene mutations were found, including 11 single‐site mutations and 6 double‐site mutations. Considering the significant differences in G6PD activity, the cut‐off value was detected to be 2.35 and 3.65 U/gHb for males and females, respectively. Significant differences in G6PD activities were noted and found to be varied from 4.61 to 6.02 U/gHb in different seasons (p < 0.0001). G6PD deficiency screening is a significant detection test for neonatal G6PD deficiency prevention. Our study highlights that the screening should be done using different cut‐off values according to the sexes in different seasons.