Ｏｂｊｅｃｔｉｖｅ　To observe the effects of dexamethasone on ultrasound-guided transversus abdominis plane block (TAPB) for laparoscopic-assisted radical operation of colorectal cancer.　Methods　Ninety patients scheduled laparoscopic-assisted surgeries for colorectal cancer were randomly divided into 3 groups. Patients in group C only received general anesthesia. Patients in group T were given ultrasound-guided TAPB after the induction of anesthesia. Patients in group TD were administrated with 10 mg dexamethasone intravenously before the induction of anesthesia, and then received TAPB. Pethidine was given when numerical rating scale(NRS) pain score was higher than 3, a sign for the requirement of postoperative rescue-analgesia. In this study, we assessed the total consumption of remifentanil and sevoflurane during operation. NRS pain scores were assessed at 2, 6, 12, 24, 48 h after the operation. The first?蛳time administration and consumption of pethidine were recorded. We also recorded incidence of adverse reactions.　Results　Compared with group C, the consumption of remifentanil and postoperative NRS pain scores at all time points were significantly less in group T and group TD(P<0.05), the first-time administration of pethidine was delayed and the consumption of pethidine was also less(P<0.05) in group T and TD. Incidence of postoperative nausea and vomiting(PONV) in group T and TD was declined(P<0.05). Compared with group T, group TD had lower NRS scores at 6, 12 h after the operation, delayed first-time administration of pethidine, and less consumption of pethidine(P<0.05).　Conclusions　TAPB combined with dexamethasone intravenously will prolong the time of blockade. Reduction of the total consumption of opioids in laparoscopic-assisted surgery for colorectal cancer was also significant.