The body colour of this species is variable from grey to brown to black, with white spots or stripes.

[6] This species should not be confused with the monocled cobra (Naja kaouthia), which has similar habitat, size and appearance.

Although Wüster (unpublished) reports that N. siamensis readily spits and may have a longer range, closer to 2 metres (6.6 ft), which comes out in a stream.

The specific epithet siamensis is derived from the word Siam or Siamese, which means "relating to or characteristic of Thailand or its people and language".

However, when the snake is threatened at night, it is more aggressive and is more likely to stand its ground, rear up and display its hood and spit out its venom.

Hatchlings are anywhere from 12 to 20 cm long and, because they possess fully developed venom delivery systems, should be treated with the same respect as adults.

[4] Like all cobras, this species shows variation in venom toxicity based on different factors (diet, locality, etc.).

Deaths, which generally happen due to paralysis and consequent asphyxiation, mainly occur in rural areas where the procurement of antivenin is difficult.

Local swelling and necrosis were common, but many of the patients were followed up for too short a time to allow precise assessment of the incidence of these effects.

Swelling and necrosis, comparable in all respects with that following bites by N. kaouthia, in patients envenomed by N. siamensis in Ubon and Kanchanaburi in Thailand.