Objective: We investigated the proinflammatory functions of endoplasmic reticulum stress and peroxisome proliferator-activated receptor α (PPARα) in the development of gestational diabetes mellitus (GDM) and their relationship in regulating inflammation in GDM. Methods: This study was performed on placentas of normal pregnant women, women with GDM, and HTR8 cells. Transmission electron microscopy, immunohistochemistry, Western blot analysis, and RT-PCR were performed to analyze ERS and PPARα expression on both normal and GDM pregnancy placentas. ELISA was performed to analyze inflammatory biomarkers. To generate models of the GDM-like state, placentas of normal pregnancy were treated with LPS and polyinosinic-polycytidylic acid (poly [I:C]). TG, CHOP plasmid, and CHOP siRNA were assessed as to their regulation of HTR8 cells to discern the relationship between ERS and PPARα in regulating the inflammation associated with GDM. Results: ERS was elevated in GDM placentas, induced the secretion of IL-6 and TNF-α, and attenuated the expression of GLUT-4. PPARα was diminished in GDM placentas and inhibited the inflammatory responses via the NF-κB nuclear-transport process. 4-PBA reduced CHOP and augmented PPARα, and it decreased IL-6 and TNF-α in our GDM-like explant. However, with both 4-PBA and MK886 treatment, we noted no significant difference in CHOP expression. The level of PPARα was reduced, and that of NF-κB p65 in the nucleus was elevated with TG treatment in the HTR8/Svneo. Knockdown of CHOP increased PPARα and reduced NF-κB p65, while expression of PPARα declined, and that of NF-κB p65 rose with the application of CHOP when HTR8 cells were treated with TG. Conclusions: ERS contributes to the pathophysiology of GDM in pregnancy via the CHOP-PPARα–NF–κB-signalling pathway by inducing aberrant activation of inflammation and insulin resistance.