An illuminated modular dog leash and collar assembly includes electrically mated segments connected end-to-end and defining a rectilinear shape. Each of the segments includes illuminable light-emitting sources housed therein and connected in sequence, a tubular core, and a sleeve removably positioned about the core. The sleeve extends along the entire longitudinal length of the modular segment associated therewith. An extendable handle is removably attached to the leash and spaced from the collar, and is adaptable between alternate longitudinal lengths. A mechanism independently illuminates the light-emitting sources such that the collar and leash selectively illuminate when the pet becomes separated from the caregiver beyond a predetermined distance.