Pharmacist''s contribution to the promotion of access and rational use of essential medicines in SUS. Objective::  to describe the pharmaceutical inclusion process in a Basic Health Unit multidisciplinary team and evaluate results related to rational use and promotion of access to essential medicines. Methods::  This is a descriptive, cross-sectional study conducted in a primary care health unit in the city of São Paulo. Pharmacist''s activities were evaluated regarding the service structure and organization and prescribing quality improvement, guidance method creation, and implementation of clinical pharmacy service. Data measured before and after the interventions and between 2010 and 2011 were analyzed using Pearson´s chi-square test with a significance level of 5%, and odds ratio. Results::  Pharmacist''s activities had statistically significant result in drug shortage reduction; prescribing quality improvement associated with an increased proportion of prescriptions met; decrease in the total of prescribed drugs among patients receiving pharmacotherapeutic follow-up and, comparing the years 2010 and 2011, changes in the pharmacotherapy recommendations have gained increased acceptance level. Conclusions::  Pharmacist''s activities may effectively provide rational use and promotion of access to essential medicines.