Preheat oven to 425 degrees F.
In a large bowl, whisk together balsamic vinegar, brown sugar, olive oil, salt and pepper. Add green beans and toss to coat well.
Pour green beans out onto a foil-lined baking sheet. Spread out green beans into an even layer and drizzle with remaining oil mixture.
Roast in oven for 15 minutes; remove and toss green beans again. Return to oven for an additional 15 minutes. (Most of the balsamic should be caramelized by now and a glaze will form on the beans.)