The variations of the orbital period of the RS CVn-type binary system SZ Psc are examined through a detailed description of the O-C diagram and the use of a new analysis technique. Continuous changes of very large magnidude have been found. They are considered as short-timescale variations whose character is investigated for periodicity or as short-timescale variation of periodic and non-periodic behaviour eventually carried by an underlying long-timescale variation. The prospective physical mechanisms that could have modulated the orbital period in the observed way, have been examined for both cases. A combination of a magnetic activity cycle mechanism and an enhanced stellar wind are found to reproduce satisfactorily the period changes. Key words: orbital period variations - mass transfer - mass loss - third body - magnetic activity