Several attempts to decrease sugar demand by introducing stevioside as a sugar substitute in children's food products have been made, but safety issues were concerned. This exploratory study investigated the effects of stevioside low dose (SL), high dose (SH) and low dose with inulin (SL + I) for 12 weeks on the body weight, organ relative weight, hematological and biochemical parameters and enzyme activities of young male rats. The SL dose used in this study was 15 mg kg−1 per day and the SH dose was 100-fold the low dose. Enormous similarities in most parameters were observed with no significant differences between SL, SL + I and control except in the lipid profile. Total lipid reduction in SL and SL + I and significant high-density lipoprotein increase in SL + I were observed, which may be considered as clinically beneficial. Significant decreases in serum tartrate-resistant acid phosphatase activity were also observed in all treatments. Treatment with SH caused significant changes in all investigated toxicological parameters. The results indicated that, although the SL dose was higher than the stevioside temporary accepted daily intake (5.0 mg kg−1 body weight), no toxicological effects were observed in SL or SL + I on body weight, organ relative weight, hematological and biochemical parameters or enzyme activities investigated in this study, whereas stevioside high dose (1500 mg kg−1 per day) may be considered as a toxic dose for the same biological parameters in young male rats. However, the effects of SL, SH and SL + I on serum tartrate-resistant acid phosphatase activity need more investigation. Copyright © 2010 John Wiley & Sons, Ltd.