To investigate the correlation between endoplasmic reticulum (ER) stress and growth hormone (GH) secretion in pituitary GH adenomas and its mechanism. Methods: The clinical data of 20 patients with pituitary adenomas treated by transsphenoidal approach in the Department of Neurosurgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology from September 2021 to November 2022 were analyzed retrospectively. The tumor tissues were collected and sections were made for immunohistochemical staining. The correlation between the expression of ER stress protein and the preoperative GH level was analyzed. The tumor tissues of patients were extracted for primary culture and intervened with ER stress stimulants Tm、Tg and ER stress inhibitor 4-PBA to detect the changes of GH secretion and pituitary specific transcription factor (PiT-1) expression in GH adenoma cells. Results: (1) Expression levels of GRP-78, XBP-1s and p-eIF-2α were all positively correlated with preoperative GH level (all P<0.0001). (2) ER stress stimulants Tm and Tg promoted the secretion of GH in GH adenoma cells (both P<0.001). (3) ER stress inhibitor 4-PBA could significantly reduce the promoting effect of Tm on GH secretion in GH adenoma cells (P<0.0001). (4) ER stress stimulators Tm and Tg promoted the expression of PiT-1 gene at both the transcriptional level (Tm group P<0.001, Tg group P<0.0001) and the translational level (Tm group P=0.0093, Tg group P<0.003) in GH adenoma cells. (5) ER stress inhibitor 4-PBA could significantly reduce the promoting effect of Tm on PiT-1 gene expression in GH adenoma cells at both transcriptional level (P<0.0001) and translation level (P<0.0001). Conclusion: There was a significant positive correlation between ER stress and GH secretion in pituitary GH adenomas. ER stress could promote GH secretion in GH adenoma cells, and inhibition of ER stress could reduce GH secretion. ER stress could promote PiT-1 expression in GH adenoma cells, and inhibition of ER stress could reduce PiT-1 expression in GH adenoma cells.