The small mammals, especially rats are pest species that are present in cities world-wide. The rat moves around and into residences and other anthropogenic structures. It is especially ubiquitous in urban slums and a threat to infrastructure and public health due to the pathogens it carries and transmits. Effective control of rat populations in most urban areas has been unsuccessful, despite several rodent control efforts. Limited information about rat movement distance has hindered identification of control units and effective scales at which to enact control during interventions. We evaluated the suitability of Rhodamine B, a non-toxic biomarker, for assessing the distance travelled by rats in urban slums. We tracked rats over two campaigns between 2019 and 2020. Overall, 27.9% of trapped rats showed signs of Rhodamine B in their whiskers under fluorescence microscope. This shows that our method provides a viable alternative for investigating the movement of small mammals in this area. We found that rats move up to 90 m distance in urban slums, with smaller rats travelling more actively than bigger rats. Information obtained from this study should be useful in guiding efficient rodent control initiatives to reduce the risk of household rodent infestation and rodent-borne disease in urban slums.