Sea cucumber is a valuable resource containing several materials that can be used as natural products and pharmaceutical industries. In this study, proximate composition and the amount of total phenols, flavonoids and antioxidant activity of fresh and rehydrated (after drying) sea cucumber, Holothuria parva, were examined. The samples were collected from Bandar Lengeh in the Persian Gulf during low tide and kept frozen. The samples were freeze-dried and the moisture content was calculated. The protein, lipid, ash and carbohydrate contents were then measured. The amounts of antioxidant activity (DPPH), phenol and flavonoid contents were also measured. All results have possibility (p<0.05). In fresh sample, the moisture, protein, lipid, ash and carbohydrate contents were ±81.20, ± 12.00, ± 0.34, ±5.50 and ±0.95%, respectively, while they were ±92.50, ± 3.76, ±0.36, ±1.00 and ±2.07% in rehydrated sample. The antioxidant activity in fresh and rehydrated samples were equal to ±0.063 and ±0.060 mg vitamin C/g dry sample, respectively. The IC50 in fresh sample was ±5.26 while in the rehydrated sample was ±4.14. Total phenol content of fresh and rehydrated samples were equal to ±0.22 and ±0.19 mg gallic acid/g dry sample, repectively. The flavonoid contents in fresh and rehydrated samples were equal to ±3.86 and ±5.02 mg Quercetin/g dry sample, respectively. The amounts of protein and ash in fresh sample were significantly higher than rehydrated sample with significant difference (p<0.05). Moisture in rehydrated sample was significantly higher than fresh sample with significant difference (p<0.05). There were no significant difference between fresh and rehydrated samples in terms of their phenon and flavonoid contents. The DPPH radical scavenging capacity was significantly higher in the fresh sample compared to the rehydrated sample with significant difference (p<0.05). It can be concluded that this species of fresh sea cucumber has more antioxidant activity than rehydrated (after drying) sea cucumber and more beneficial to be used in pharmaceutical and food industries.