In Algeria steppe (Rogassa), the overgrazing leads to reduction the surface of pasture land and biodiversity too. The objective of this work is to highlight the importance of protected land in maintaining biodiversity and preserving degraded areas. We adopted a mixed sampling for two different sites, of which we conducted fifty floristic surveys using the Braun-Blanquet. The analysis of the real biological spectrum of unprotected land is marked by the strong dominance of Therophytes. However, in protected lands, the Chamaephytes dominate all biological types. Analysis of biogeographic spectra reveals the reappearance of endemic species (+3%). The Shannon Index is very important (2.43). The Student’s t-test of biodiversity’s index shows a highly significant difference between the two sites. The ascending hierarchical classification reveals that the protected land is subdivided into four groups dominated respectively by: Macrochloa tenacissima, Lygeum spartum, Artemisia erba-alba and Hordeum murinum. The results of the Jaccard dissimilarity index indicate a strong difference of the order of 80% between the two areas.