Background: Anadenanthera colubrina (Vell.) Brenan var. cebil (Griseb) is a plant widely used for medicinal proposes in Brazilian Northeast. Objective: This study aimed to analyze the influence of rainfall indexes (RI) in antimicrobial activity and phytochemical constituents of extracts from leaves and fruits of A. colubrina. Material and Methods: Samples were collected in Catimbau National Park (Buíque, Pernambuco, Brazil) at September 2010 (RI: 75 mm) and January (RI: 65 mm), April (RI: 162 mm) and June 2011 (RI: 73 mm). The extracts were prepared by Soxhlet extraction using cyclohexane, chloroform, ethyl acetate and methanol. The antimicrobial activity was determined by MIC and MBC values. Results: All extracts showed antimicrobial activity, but ethyl acetate extracts (from all periods) were more active. Strong correlations were found between the RI and the average MIC of MLE (ρ: -0.99), EALE (ρ: -0.81), CHFE (ρ: -0.81), EAFE (ρ: -0.80); while moderate and weak correlations were found for other extracts. Through a HPLC analysis was possible to reveal that the samples collected from dry periods had more chemical diversity (as they presented more peaks). Gallic acid and quercetin (and derivative compounds) were identified. The levels of quercetin were enhanced in extracts from dry months. Conclusion: Our results showed that the rainfall has a positive effect on the antimicrobial activity of leaves and fruits of A. colubrina, however these extracts showed more chemical diversity during dry months.