Facial soft tissues have different thicknesses among different genders and ethnicities. This study was aimed to investigate the association of sex, ethnicity and body mass index (BMI) with facial soft tissue thickness measurements using magnetic resonance imaging to make a database for the Iranian southwest population (for Lur and Arab populations). In this analytical cross-sectional study, measurements of superficial soft tissues were taken at nine points of midline including glabella (GB), nasion (NA), end of nasals (END), mid-philtrum (MID), upper lip margin (UL), lower lip margin (LL), chin-lip fold (CLF), mental eminence (ME) and beneath chin (BC), eight points of axial sections including frontal tubers (FT), supraorbital margin (SO), external orbital margin (EX) and zygomatic arch (ZY) on both sides, and also two points of coronal section including both sides of the masseteric region (MST). For association of sex with the measurements, NA, MID, UL, LL and BC were significantly higher in men (Pc < 0.05). The most accurate measurement was MID with area under curve (AUC) = 85.03%, followed by UL (81.21%), NA (72.18%), LL (71.19%) and BC (68.10%). For association of ethnicity with BMI and measurements, higher amounts of GB and MID were associated in Arab patients. This study showed significant association of soft tissue thickness measurements with sex, BMI and ethnicities of southwest of Iran. MID had the most diagnostic value for male sex. The results of this study can be used in forensic medicine to diagnose the legal and biological identity of the corpse.