Microbial biomass plays key roles in the ecosystem sustainability by maintaining essential functions of soil health, through carbon and nutrient turnover. Species richness and diversity of plant functional groups can influence microbial biomass. Thus, it is necessary to study how different intercropping systems affect soil biological parameters to predict potential benefits of their implementation. Thus, the objective of this study was to evaluate the effect of intercropping leguminous trees with forage cactus on soil microbial biomass in the semi-arid tropic of Pernambuco. The experiment (8 years) was conducted on a Regosol soil at Caruaru Experimental Station, Agronomic Institute of Pernambuco - IPA (8º 14’ S and 35º 55’ W). The following cropping systems were tested: i) Gliricidia [Gliricidia sepium (Jacq.) Kunth] + forage cactus IPA Sertânia [Nopalea cochenillifera (L.) Salm-Dyck], ii) forage cactus IPA-Sertânia. Treatments were allocated in a randomized complete block design, with four replications. Soil samples were collected seven years after the implementation of the systems, at 0- to 10-cm layers, during the dry period (October 2018). Samples were used to determine the microbial quotient (qMIC) and mineralization quotient (qM). The soil of the agroforestry system and cactus monoculture had similar qMIC (1.4 and 2.3%) and qM (3.7 and 3.9%), respectively. qMIC values > 1% indicate a favorable condition for microbial activity. In both cropping systems, the qM indicated a better efficiency of microorganisms in metabolizing organic matter. The different cultivation systems provided a beneficial environment for microbial activity