  In supersymmetric theories, the main decay modes of scalar quarks are decays
into quarks plus charginos or neutralinos, if the gluinos are heavy enough. We
calculate the O($\alpha_s$) QCD corrections to these decay modes in the minimal
supersymmetric extension of the Standard Model. In the case of scalar top and
bottom quarks, where mixing effects can be important, these corrections can
reach values of the order of a few ten percent. They can be either positive or
negative and increase logarithmically with the gluino mass. For the scalar
partners of light quarks, the corrections do not exceed in general the level of
ten percent for gluino masses less than 1 TeV.
