Objectives: To preserve olfactory function in each nostril following pituitary surgery is important in the long term. However, no reports evaluating olfactory outcomes in individual nasal cavities following endoscopic endonasal transsphenoidal approach (EETSA) for pituitary surgery have been published. Here, we used an endoscopic modified transseptal bi-nostril approach for pituitary surgery, with possible olfaction preservation without turbinate resection, and evaluated olfactory outcomes in both left and right nostrils. Design: A single-centre, retrospective study Setting and participants: Overall, 41 patients who underwent endoscopic modified transseptal pituitary surgery with an olfactory and turbinate preservation approach at our hospital between April 2018 and December 2019 were included in this study. Main outcome measures: To completely protect the bilateral turbinates and olfactory epithelium, this procedure provides access to the sphenoid sinus by a transseptal approach via the left nasal cavity and by the olfactory cleft approach via the right nasal cavity without resecting any turbinate. A jet stream olfactometer (JSO) was used to assess the mean recognitive threshold of the left, right, and bilateral nasal passages before and after surgery. Results: The postoperative JSO test values of the right, left, and bilateral nasal cavities were markedly improved (p<0.01 for all) compared with the preoperative values, but there was no difference in the values between the right and left nasal cavities (p=0.85). No recurrence or olfactory dysfunction was observed in any patient during the study period. Conclusion: Our modified EETSA may be one method to approach preserving every turbinate and olfaction.