Background and purpose: Population aging is one of the most important issues in demography that has attracted much attention. In Iran, the population is changing from young structure to an old structure. This fast transition calls for designing studies about population ageing in all provinces. This study was conducted to determine the population structure in Mazandaran province. 

Materials and methods: Four census data sources (1986 to 2011) were used and population ageing index was calculated by median age, fertility and mortality rates. Hierarchical cluster analysis which is an unsupervised classification method was used for grouping the cities in R package version 3.1-2 and thematic mapping was prepared using GIS software 10.

Results: The number of clusters of cities considering population aging index, median age of the indices, general fertility and mortality rates in the census of 1986 and 1996 was 6 and in next censuses was 5. In all four censuses the highest aging index and the least number of cluster index were greater than the value of country’s old population. Bar graph indicator of the aging population showed a significant increase in the index during the 1986-2011 censuses.

Conclusion: According to the results, population aging was found to have a dramatic increase in Mazandaran province during the censuses. This increase may have different reasons and could not be only due to decline in fertility rate. In some towns such as Savadkuh emigration from the region could be responsible for the increase of ageing population. Another cause of this increase in the province could be increase of life expectancy. Therefore, appropriate planning is required on this subject.