I have used it while raining once, it worked great that night, but this was only 2 hours after the deer was shot, it started raining just after shot, it had made the blood trail hard to find. This stuff lit the trail up nice! But after 3 or 4 rains, I really don't think it's gonna work, but hey, what do ya have to lose.....20 bucks at most right? By the way, it has to be pretty dark before this stuff lights up very well, the darker the better.