OBJECTIVE The purpose of this 3-arm parallel trial was to compare the effects of tooth tissue-borne (TTB), tooth-borne (TB) and bone-borne (BB) rapid maxillary expansion (RME) appliances on nasal airway with acoustic rhinometry (AR). METHODS Forty-six 12- to 14-year-old patients with narrow maxilla were randomly allocated into 3 study groups accordingly the type of expander: TTB, TB and BB. The participants were recruited from the Department of Orthodontics, Izmir Katip Celebi University. METHODS All patients had RME with an initial activation of two-quarter turns a day (0.5 mm) for an average of 8 days followed by 1 quarter turns per day for an average of 10 days. Disguised group allocation using opaque sealed envelopes was made with a computer-generated randomization program. The primary outcome was changes on the minimal nasal cross-sectional area (MCA). Secondary outcome included the assessment of nasal cavity volume. AR measurements were obtained at baseline (T0), immediately after the expansion (T1), and at 3 months-follow-up (T2). One-way analysis of variance (ANOVA) and Bonferroni test were used for inter-group comparison and two-way ANOVA was used for intra-group evaluation. RESULTS There were significant increases in MCA 1, 2 and nasal Vol in all groups after the treatment (95% [CI], P < 0.05) whereas in inter-group comparisons; MCA 1, 2 and nasal Vol, the changes were found to be similar (95% [CI], P > 0.05). RESULTS No serious harm was observed except for mild gingivitis due to plaque accumulation. CONCLUSIONS RME treatment increased minimal nasal cross-sectional areas and nasal volume irrespective of appliance design. BACKGROUND This trial was registered at Clinicaltrials.gov (Identifier NCT04529057). METHODS The protocol was not published. BACKGROUND This trial was financed by Izmir Katip Celebi University, Scientific Research Projects Unit [grant number 2016-TDR-SABE-0024].