Understanding the relationship between litter quality and macrodetritivore feeding performances is of prime importance. Among soil invertebrates, macrodetritivores such as millipedes (Diplopoda) and terrestrial isopods (Crustacea, Isopoda) could play a significant role in the decomposition process. Furthermore, studies relating herb litter to macrodetritivore performances (consumption, dejection, assimilation) are scarce and rarely used litter traits (especially no physical trait). We thus design a laboratory experiment to answer the following question : what are the pivotal chemical/physical traits informing litter grass quality that shape such macrodetritivore performances? The performances of two common macrodetritivores Armadillidium vulgare (Latreille, 1804) and Glomeris marginata (Villiers, 1789) on heterogeneous litter coming from perennial forage grasses to have a wide spectrum of functional profiles (Brachypodium pinnatum P. Beauv., Bromus erectus Huds., Festuca rubra L. and Holcus lanatus L.) were assessed. We used litter traits to inform litter quality. We also used some conservative plant traits. A. vulgare performances were correlated with nutrient aspects (litter N and P contents) and plant mechanical aspects (leaf dry matter content). G. marginata performances were correlated with plant fiber contents (cellulose and lignin contents).