BackgroundPublic health policies and healthcare quality play a pivotal role on the health outcome level and disparities across sociodemographic groups. However, there is little evidence on their role on disparities in life expectancy (LE) and life disparity (LD) in low and middle income countries. The present study aimed to assess the contributions of avoidable mortality, as a measure of inter-sectoral public health policies and healthcare quality, into the sex gap in LE (SGLE) and LD (SGLD) in Iran.MethodsLatest available data of death causes, according to the ICD codes, for Iran was obtained from the WHO mortality database for the period 2015–2016. An upper age limit of 75 years was applied to define avoidable causes of death. LD was measured as the average years of life lost at birth. The SGLE and SGLD (both females minus males) were decomposed by age and cause of death using a continuous-change model.ResultsFemales, on average, outlived males for 3.8 years (80.0 vs. 76.2 years) with 1.9 lower life years lost (12.6 vs. 14.4 years). Avoidable causes accounted for 2.5 (67%) and 1.5 (79%) years of the SGLE and SGLD, respectively. Among avoidable causes, injury-related deaths followed by ischaemic heart disease had the greatest contributions to both SGLE and SGLD. Across age groups, the age groups 55–59 and 60–64 accounted for the greatest contributions of avoidable causes to SGLE (0.3 years each), while age groups 20–24 and 55–59 had the greatest contributions to SGLD (0.15 years each). Lower mortality rates for females than males in age groups 50–74 years accounted for about half of the SGLE, while age groups 20–29 and 50–64 years accounted for around half of SGLD.ConclusionMore than two third of the SGLE and SGLD in Iran were attributed to the avoidable mortality, particularly preventable causes. Our results suggest the need for public health policies targeting injuries in young males as well as lifestyle risk factors including smoking in middle aged males in Iran.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13690-023-01141-z.