Importance: During hospitalization for hematopoietic stem cell transplantation (HCT), patients receive high-dose chemotherapy before transplantation and experience significant physical and psychological symptoms and poor quality of life (QOL). Objective: To assess the effect of inpatient palliative care on patient- and caregiver-reported outcomes during hospitalization for HCT and 3 months after transplantation. Design, Setting, and Participants: Nonblinded randomized clinical trial among 160 adults with hematologic malignancies undergoing autologous/allogeneic HCT and their caregivers (n = 94). The study was conducted from August 2014 to January 2016 in a Boston hospital; follow-up was completed in May 2016. Interventions: Patients assigned to the intervention (n=81) were seen by palliative care clinicians at least twice a week during HCT hospitalization; the palliative intervention was focused on management of physical and psychological symptoms. Patients assigned to standard transplant care (n=79) could be seen by palliative care clinicians on request. Main Outcomes and Measures: Primary: change in patient QOL from baseline to week 2; secondary: patient-assessed mood, fatigue, and symptom burden scores at baseline, 2 weeks, and 3 months after HCT and caregiver-assessed QOL and mood at baseline and 2 weeks after HCT. Results: Among 160 enrolled patients (mean age, 60 [SD, 13.3] years; 91 women [56.9%]; median hospital stay, 21 days) and 94 caregivers, 157 (98.1%) and 89 (94.7%), respectively, completed 2-week follow-up, and 149 patients (93.1%) completed 3-month follow-up. Patients in the intervention group reported a smaller decrease in QOL from baseline to week 2 (mean baseline score, 110.26; week 2 score, 95.46; mean change, -14.72) compared with patients in the control group (mean baseline score, 106.83; week 2 score, 85.42; mean change, -21.54; difference between groups, -6.82; 95% CI, -13.48 to -0.16; P = .045). Among the secondary outcomes, from baseline to week 2, patients in the intervention group vs those in the control group had less increase in depression (mean, 2.43 vs 3.94; mean difference, 1.52; 95% CI, 0.23-2.81; P = .02), lower anxiety (mean, -0.80 vs 1.12; mean difference, 1.92; 95% CI, 0.83-3.01; P < .001), no difference in fatigue (mean, -10.30 vs -13.65; mean difference, -3.34; 95% CI, -7.25 to 0.56; P = .09), and less increase in symptom burden (mean, 17.35 vs 23.14; mean difference, 5.80; 95% CI, 0.49-11.10; P = .03). At 3 months after HCT, intervention patients vs control patients had higher QOL scores (mean, 112.00 vs 106.66; mean difference, 5.34; 95% CI, 0.04-10.65; P = .048) and less depression symptoms (mean, 3.49 vs 5.19; mean difference, -1.70; 95% CI, -2.75 to -0.65; P = .002) but no significant differences in anxiety, fatigue, or symptom burden. From baseline to week 2 after HCT, caregivers of patients in the intervention group vs caregivers of patients in the control group reported no significant differences in QOL or anxiety but had a smaller increase in depression (mean, 0.25 vs 1.80; mean difference, 1.55; 95% CI, 0.14-2.96; P = .03). Conclusions and Relevance: Among adults at a single institution undergoing HCT for hematologic malignancy, the use of inpatient palliative care compared with standard transplant care resulted in a smaller decrease in QOL 2 weeks after transplantation. Further research is needed for replication and to assess longer-term outcomes and cost implications. Trial Registration: clinicaltrials.gov Identifier: NCT02207322.