Background: Poor quality products, adverse drug reactions (ADRs) and medication errors (ME) are reported to negatively influence health care cost, patients’ treatment outcomes and quality of life. One way which can help in detection and prevention of their occurrence is through spontaneous reporting of these effects/events to the regulatory bodies. Despite the efforts done by regulatory bodies in different countries including Tanzania, the rate of reporting has remained low. This study therefore, assessed the participation of private healthcare facilities in pharmacovigilance (PV) activities in Tanzania Mainland. Methods: A descriptive cross sectional study was conducted in selected regions in Tanzania from December 2017 to June 2018. A total of 169 healthcare facilities and 192 healthcare professionals were involved. Data was collected using questionnaires and standard checklist. Results: Only (17%) of the respondents had good knowledge on PV activities and only (29.7%) of the participants had attended training on PV. Over 50% of respondents were not aware that PV activities reports are to be sent to a National pharmacovigilance center. Majority (89.7%) of the healthcare facilities assessed had no system for monitoring and reporting PV activities. About (55.7%) of the respondents said that they had observed ADRs in patients while (27.6%) had detected poor quality products and (51.1%) spotted medication errors in their practice, but none of them sent a report to the National pharmacovigilance center. Lack of PV tools (60.9%), poor knowledge on reporting procedures (69.8%) and lack of feedback and weak supervision from Tanzania Medicines and Medical Devices Authority (TMDA (93.3%) and (9.4%), respectively were the major obstacles for carrying out PV activities. Of the 47 respondents whereas, their healthcare facilities had systems for monitoring and reporting PV activities had a view that attending more training (74.5%), increase availability of PV tools (10.6%), frequent supervision from TMDA (12.8%), and inclusion of PV training in undergraduate and postgraduate training curricula (2.1%) may improve involvement in pharmacovigilance activities Conclusions: Majority of private healthcare facilities participated poorly in PV activities, because of lack of pharmacovigilance training, knowledge on reporting and unavailability of systems and tools for monitoring and reporting on pharmacovigilance activities.