Injections of the toxin were found to halt the shaking or tremor in the arms and hands of patients. The study, published in the journal Neurology, suggests new treatments could be developed.
Tremor affects two thirds of patients with MS, yet evidence for current treatments is mixed.
Previous research had suggested botulinum toxin could reduce tremors but concerns persisted over side-effects, including loss of muscle strength.
Researchers led by Dr Anneke van der Walt of the University of Melbourne, Australia gave botulinum toxin type A or placebo injections to 23 patients with MS for three months.
Treatment was then reversed for the next three months.
Researchers measured the severity of tremors, including patients' ability to write and draw before, during and after treatment.
They detected ‘significant improvement’ in tremor symptoms among those receiving botulinum injections.
Severity fell markedly, from moderate to mild as measured by a clinical score. Writing and drawing ability improved by around one point on a 10-point scale.
Muscle weakness, the only side-effect, developed in 42% of patients on botulinum injections compared with 6% on placebo. But this was mostly mild and faded within two weeks.
Dr van der Walt said: ‘Our study suggests a new way to approach arm tremor related to MS where there are currently major treatment challenges and it also sets the framework for larger studies.’