In order to survey on effects of  dietary Thyme (Thymus vulgaris) extract on common carp 180 Fish with average weight of 10.84±0.063 were divided into four groups  with three replicates (each replicate with 15 fihs), and fed with different levels of dietary Thyme extract including 0, 0.5, 1 and 2 % for 70 days. At the end of rearing period 30 fish from each group were exposed to 13 ppt sea salt for 12 hours and were studied for hematological parameters. In this regard, sampling were done in times of  before salinity stress and 6, 24, 72 hours post salinity stress from caudal peduncles.  In this study supplementary thyme extract in food has no effects on growth performance after rearing period (P>0.05). in hematological study, after salinity stress hematocrit levels in treatments 0.5 % was increased compared to control group (p<0.05). And so hematocrit value in fish of treatments 1% and 2% groups were calculated significantly higher compare with control,  72 h post salinity stress (p<0.05). Hemoglobin levels just in the treatment groups were significantly increased after salinity stress  (p<0.05).The white blood cells (WBC)  and red blood cell (RBC)counts and so hematological indices (MCV, MCH, MCHC value) had no significant difference among all studied fish (P>0.05). Totally in this study supplementary 0.5, 1 and 2 % dietary thyme extract has no effect on growth performances and hematological parameters in common carp in salinity stress situation.