Natural products derived from plants, fungi, bacteria and marine organisms are discovered extemporaneously and have a long practice in medicine. Till date, the exploit of natural products, their semi synthetic and synthetic derivatives have been restrained largely to their ethnic use. However, it has been well recognized that each substance has a broad spectrum of biological activities as apparent from some new uses of several old drugs. Prediction of Activity Spectra for Substances (PASS) has been utilized as a potential tool to predict the biological activity spectrum of synthetic substances for the detection of new drugs. The present study was therefore undertaken to examine the biological activity spectrum of the phytoconstituents of Callistemon citrinus with their reported biological activities in order to evaluate the applicability of PASS. Subsequently, Molinspiration was utilized to evaluate the oral bioavailability of compounds in order to select the promising compounds that have higher odds of not being discarded in the clinical phase. © 2016, Global Research Online. All rights reserved.