Identifying nonrandom species composition patterns predicted by assembly rules has been a central theme in community ecology. Few studies have investigated the prevalence of multiple drivers on species composition patterns in small mammal assemblages in the Old World. This study investigated seasonal changes in rodent and shrew diversity in eleven savannah vegetation types in South Africa. We tested whether species composition patterns are nonrandom with respect to predictions from Diamond's assembly rules, niche limitation hypothesis and nestedness hypothesis. Species richness estimators indicated that inventories for the rodents (80%) and shrews (100%) were relatively complete. Rodent (n = 11 species) diversity and shrew (n = 5 species) diversity were highest in summer and lowest in autumn. Rodent richness was highest in the Terminalia sericea bushveld and woodlands and lowest in the Drypetes arguta sand forest, whilst shrew richness was highest in the T. sericea bushveld and woodlands and lowest in the Acacia nilotica/Dichrostachys cinerea open shrub savannah. We found no support for the predictions of competition and nestedness hypotheses and suggest that this was probably due to the high seasonal and annual variability in rodent and shrew diversity. rongeurs etait la plus haute dans la brousse a Terminalia sericea et la forêt, et la plus faible dans la forêt sableuse a Drypetes arguta, alors que la richesse en musaraignes etait la plus elev ee dans la brousse a T. sericea et la forêt, et la plus faible dans la savane arbustive ouverte a Acacia-nilotica/ Dichrostachys cinerea. Nous n'avons rien trouv e qui vienne etayer les pr edictions des hypoth eses de comp etition et d'« imbrication », et nous sugg erons que c'est probablement dû a la forte variabilit e saisonni ere et annuelle de la diversit e des rongeurs et des musaraignes.