i weight train twice a week and am currently trying to gain weight. i am 5'9 154lb. i am thinking about joining a boxing club for self defence/fitness ect and was wondering if this would interier with my muscle building. thanks for any replies

if you do resistance training at the boxing it might, but i think boxing is mostly cardio. you use muscles when you hit, but hitting is considered so high rep that its really just cardio
im no expert so you might want a secound opinion.

Karky is right.

The cardio still however takes away from your energy source to muscle build, or even yet you could be burning protein.

Make sure you drink some drink that is high in carbs, sugars, ect. so that you get another energy source so you don't burn the essentials for muscle building.

good point Nobody! and the boxing should be done on different days, so you can restore your energy and dont confuse your energy pathways

Treat it the same as anyother sport.
Do your resistance training and boxing at oposite ends of the day, or on diffrent days.