The short answer
The brown rat, also known as the Norway rat, is the large rat most commonly seen in Hong Kong — noticeably big-bodied (around 20 to 25cm not counting the tail), with a blunt nose, small ears, a tail shorter than its body, and greyish-brown fur. It mainly lives in drains, refuse rooms and back lanes, and enters flats through pipework, air-conditioner conduits and wall gaps. It gnaws on wiring and packaging, and its droppings and urine carry hygiene risks. Bait alone is often not enough — rats learn quickly to avoid it, so sealing entry points matters just as much.
- Scientific name
- Rattus norvegicus
- Chinese name
- 溝鼠（挪威鼠）
- English name
- Brown rat
How to identify a brown rat
- Size: adults run about 20 to 25cm in body length excluding the tail — one of the larger rats commonly seen in Hong Kong.
- Appearance: blunt nose, small ears that sit close to the head, and coarse-looking greyish-brown fur.
- Tail: shorter than the body, darker and hairless.
- Different from the roof rat (black rat), which is smaller, has larger ears and a tail longer than its body — brown rats tend to stay at ground level and in drains, while roof rats are strong climbers that head for higher spaces.
Where do they turn up in Hong Kong homes and shops?
Brown rats mainly operate at ground level and through the drainage system:
- Drains, floor gullies, septic systems
- Refuse rooms, back lanes, storage corners in ground-floor units
- Air-conditioner conduits and external pipework joints
- Wall gaps and floor seams — a gap of around 1.3cm (about half an inch) is already enough for them to squeeze through
- Storerooms and refuse collection points near restaurants and wet markets
Why does it matter?
Brown rats gnaw on electrical wiring (a fire risk) and chew through food packaging and storage containers, and their droppings and urine carry hygiene risks — spending time in drains and refuse areas means they pick up a wide range of bacteria along the way. For restaurants and shops, an infestation also carries hygiene-inspection and reputational risk.
Does bait alone work?
Bait alone can reduce numbers, but brown rats learn quickly — once others die from a bait station, the remaining rats often become wary and avoid it, so effectiveness drops off over time. The effective approach is bait stations combined with exclusion work — finding and sealing the gaps and pipe openings they're using to get in, which is what actually stops new rats from entering. See our rodent control service for details.
How to keep them from coming back
- Keep stored items off the floor rather than piled against walls
- Keep bins covered and don't leave them out overnight
- Check air-conditioner conduits and external pipe joints — seal any gap over about 1.3cm
- Keep back lanes and shopfronts tidy to reduce hiding spots and food sources