BACKGROUND:People with hepatocellular carcinoma who undergo transcatheter arterial chemoembolization usually experience back pain due to lie supine for at least 4 hours to avoid bleeding and hematoma. Body positioning is an effective and safe method for decreasing back pain in people with transfemoral cardiac catheterization; however, its effects and safety among patients with high bleeding tendency are unknown. OBJECTIVE:To investigate whether body positioning could decrease back pain without increasing the chance of bleeding after transcatheter arterial chemoembolization. DESIGN:A single-blind randomized controlled trial (ClinicalTrials.gov No.: NCT03784469). METHODS:A total of 78 people with liver cancer who had undergone chemoembolization through the femoral artery were enrolled. Each person was randomly assigned to either the control or intervention group (each consisted of 39 participants). The control group received the usual care, remaining flat and lying in a supine position, whereas the intervention group had their positions changed in the second and fourth hour after chemoembolization. Participants' pain level was rated by using numerical rating scale -11 (score from 0 to 10), bleeding was measured by using volume of blood (cc.) in gauze and hematoma size in diameter (cm), and satisfaction was self-rated from 1 to 5. Repeated-measure analysis of variance (ANOVA) was used to compare the difference in pain levels over time within each group and independent t test to compare the mean difference of pain between groups at 5 endpoints, both methods with Bonferroni adjustment. Independent t test, chi-squared test, and Fisher's exact test compared postembolization discomfort, puncture sites bleeding, satisfaction between groups. RESULTS:Significant changes of pain levels over time in both intervention [F(2.93, 111.20)=7.64, p<.001] and control groups [F(2.66, 101.17)=20.55, p<.001]. The intervention group had a significantly lower mean pain score in the second hour (t = -2.838, p = .006) and fourth hour (t = -4.739, p < .001) when patients turning to the side than did the control group lying supine. Furthermore, patients in the intervention group had significantly higher satisfaction than did those in the control group (t = -2.422, p = .018). No hematoma and significant difference of post-procedural bleeding between groups. CONCLUSION:Changing patients' body positions in bed after transcatheter arterial chemoembolization is a safe and effective method of decreasing back pain, and increasing patients' satisfaction, without increasing the complications of bleeding and hematoma. Clinicians should change the positions of people with hepatocellular carcinoma 2 hours after they receive transcatheter arterial chemoembolization.