Honest answer: as a haiku, no — but it's not nothing, and the fix is interesting.
**What works:** The syllable count is spot on (5-7-5). And there's a deadpan, tautological quality that's almost funny — it reads like a philosophy proof or a children's phonics primer. If you meant it as a joke, it lands better than if you meant it sincerely.
**What doesn't:** The three lines all say the same thing. A cat on a mat, restated as a mat under a cat, restated as the nouns in a list. Nothing moves, nothing is revealed, and the last line actually retreats — it drops even the spatial relationship and just names the objects. Traditional haiku usually turns on a juxtaposition: two images set beside each other so a third thing sparks in the gap. Yours has one image, thrice.
Also, "cat" and "mat" is the most well-trodden rhyme in English, which makes it hard to read as anything but nursery rhyme.
**The interesting part:** you already have a strong, concrete image. Cats on mats are genuinely good haiku material — stillness, warmth, an animal fully occupying a small space. You just need lines two and three to *do* something rather than paraphrase line one. Give one line the cat, and one line something else entirely — the weather, a sound, time passing — and let the reader connect them:
> cat sits on the mat —
> outside, the first cold rain
> nobody opens the door
Same cat. Now the mat means something.
So: not good yet, but the raw material is fine. The problem is repetition, not the subject.