Despite the introduction of the ILS in Tanzania, still there is inadequate supply of essential medicine in public health facilities. The main evaluation question for this study was on the influencing factors for the performance of ILS with respect to availability of essential medicine, timeliness of delivery, order fulfillment rate, and storage practice. The specific evaluation questions were: (i) To what extent R&R forms are timely submitted? (ii) To what level are ILS tools available and utilized? (iii) To what degree are providers trained on ILS? (iv) To what scale are supervisions conducted? Descriptive cross section study design was used to study 15 public facilities in Rukwa region. These facilities included 3 health centers and 12 dispensaries from Sumbawanga district, Kalambo district, and Sumbawanga Municipal. Primary data were collected using structured questionnaires to respondents and observations using checklists. Secondary data were collected from documents and the ILS website. The findings showed that the average availability for essential commodities in the region was 78%. The average lead time (timeliness of delivery) was 75 days, and fulfillment rate was 39.7%. Timely submission of R&R forms was 46.7%. The completeness of R&R forms was 20%. Training coverage was 67%, and supervision coverage ranged from 14.7% to 27%. Hence factors affecting the performance of ILS were: Timeliness of reporting, availability and use of IS tools, training and supervision. The performance of ILS in public health facilities is still low, with respect to availability of medicine, lead time, and fulfillment rate and storage practice. If CHMTs are not putting an emphasis on making sure that R&R forms are timely submitted, ILS tools are available and utilized properly, on job training are conducted, and regular supportive supervisions are conducted, then the performance of ILS will be even worse for this reason stock out problem will never be solved.