The actress took to IG Saturday and posted a series of sexy snaps to the social media platform ... all featuring her in a tiny strapless top and matching miniskirt.

Check out the pics for yourself ... SS is rocking the clothes and hitting some suggestive poses while hanging out in her closet -- dropping to her knees in some snaps and bending at the waist in others.

She's posing with a big shoulder bag here -- and, that's the point of the whole post 'cause the bag's actually from the brand Miu Miu, as are the clothes ... and, despite being made of very little fabric, the ensemble reportedly costs around $4k.

Syndey captioned her post, "i dont do mirror selfies often but when i do they are chaotic" ... we doubt many fans will protest the chaos.

Swyndey's summer's off to an eventful start BTW ... like we've told you, Sweeney's enjoying the sun down in Florida where she recently purchased a multimillion-dollar mansion.

She's riding jet skis, banana boats down near the house ... and, just generally living it up on the East Coast -- no doubt working on her tan.