A study of 28 patients funded by Arthritis Research UK found those who pumped iron saw improvements in basic physical function, such as walking.
Researchers at Bangor and Gwynedd Hospital said such high intensity exercising could play a key role alongside drug treatment.
Experts said the exercise regime would not be appropriate for all patients.
RA is mainly a disease affecting the joints, but a less well known symptom is that it also severely reduces muscle mass and strength and this occurs even among patients whose disease is well managed.
Those with the condition are often given mild home exercises to do to stop their joints stiffening and becoming painful.
To test how effective the weight training was the researchers split the 28 participants into two groups, the Arthritis Care and Research journal reported.
One did regular weight training for 24 weeks, while the others did the less strenuous standard home exercise regimes.
They found physical function improved by between 20% to 30% in the group doing weight training. Strength also increased by nearly 120%.
A spokesman for the National Rheumatoid Arthritis Society agreed, but urged caution.
“Of course RA can affect different people in very different ways so pumping iron may not be appropriate for everyone. People should discuss [this] with their physio.”