How safe is it around union square at night

Union Square is actually right next to the Tenderloin which is known as the most dangerous neighborhoods in San Francisco. I would not recommend exploring the area around Union Square too much; though you should be okay right around the square and where all the shopping establishments are. City rules apply: don't go down dark alleys or quiet looking streets. stay where there are lots of other folks and pay attention to your surroundings.

Good luck and have fun.

Union Square is fine as long as you stay close by the square and don't go out too late at night. I would say it is fine until 10 pm most nights. It is fine in day too.

There is crime but it shouldn't be exaggerated. There is crime all over the city. Just stay in the populated well lit areas you should be fine.