what gouramis are they ?
there is a big possibility that they are both males,and if that is the case
this behaviour won't stop.
the way to tell,is by looking at the top dorsal fin,if it is pointed,then it's a male,if rounded then a female.
you can heavily plant the tank,and provide lots of floating plants,
this may help,and will give the smaller one somewhere to go,
please excuse the picture it was taken before water change day.
it's an old picture and inhabitants have changed since then. :)
anyway it's a male gourami,incase you wern't sure how to tell the difference.