Massongex (masɔ̃ʒɛ; Massongié) is a municipality in the district of Saint-Maurice, in the canton of Valais, Switzerland.
Massongex is first mentioned in 1226 as Bernardus de Massunge.
Massongex has an area, , of . Of this area, or 33.6% is used for agricultural purposes, while or 47.1% is forested. Of the rest of the land, or 15.1% is settled (buildings or roads), or 3.0% is either rivers or lakes and or 0.6% is unproductive land.
Of the built up area, industrial buildings made up 1.1% of the total area while housing and buildings made up 6.3% and transportation infrastructure made up 4.8%. Power and water infrastructure as well as other special developed areas made up 2.4% of the area Out of the forested land, 42.5% of the total land area is heavily forested and 4.2% is covered with orchards or small clusters of trees. Of the agricultural land, 20.8% is used for growing crops and 10.4% is pastures and 2.0% is used for alpine pastures. All the water in the municipality is flowing water.
The municipality is located in the Saint-Maurice district, on the left side of the Rhone river. It consists of the village of Massongex and eight hamlets including Daviaz.
The blazon of the municipal coat of arms is Gules, three Towers Argent masoned, windowed and doored Sable.
Massongex has a population () of . , 16.4% of the population are resident foreign nationals. Over the last 10 years (2000–2010 ) the population has changed at a rate of 2.6%. It has changed at a rate of 8.4% due to migration and at a rate of 4.8% due to births and deaths.
Most of the population () speaks French (1,218 or 92.3%) as their first language, German is the second most common (28 or 2.1%) and Italian is the third (24 or 1.8%).
the population was 50.2% male and 49.8% female. The population was made up of 641 Swiss men (42.0% of the population) and 125 (8.2%) non-Swiss men. There were 643 Swiss women (42.2%) and 116 (7.6%) non-Swiss women. Of the population in the municipality, 434 or about 32.9% were born in Massongex and lived there in 2000.