Abstract. – Macrobenthic communities of the Smir lagoon on the western Mediterranean Moroccan coast are described in relation to the environmental conditions. Macrofauna was organised in three communities: the Corophium acherusicum community, the Melita palmata community, and the Cyathura carinata community subdivided in two sub-communities. Results show that: (i) the distribution of macrobenthic assemblages was roughly determined by the vegetation as major structuring factor and by sediment, pH and dissolved oxygen; (ii) the overall faunal composition, species distribution and community structure in the Smir lagoon were comparable to those reported for other Moroccan brackish ecosystems; (iii) the trophic structure was exclusively dominated by detritivores and (iv), the lagoon was a slightly disturbed ecosystem with unbalanced communities.