Background & Aims: Studies have shown that blocking the PD-1/PD-L1 pathway may lead to a potential cure for HBV infections. ASC22 (Envafolimab) is a humanized, single-domain PD-L1 antibody administered subcutaneously. This study aimed to evaluate the efficacy and safety of ASC22 in virally suppressed chronic hepatitis B (CHB) patients on nucleos(t)ide analogs (NAs). Approach and Results: This randomized, single-blind, phase IIb trial enrolled CHB patients in two cohorts for a 24-week treatment with ASC22 or placebo (PBO) once every 2 weeks and 24-week follow-up. In total, 60, 59, and 30 patients were treated with 1.0, 2.5 mg/kg ASC22 and PBO, respectively. The mean HBsAg changes from baseline at week 24 and 24 week follow-up periods were -0.309 (p<0.001) and -0.272 (p<0.023) log10 IU/mL in the 1.0 mg/kg ASC22 group, -0.231 (p=0.007) and -0.205 (p=0.12) log10 IU/mL in the 2.5 mg/kg ASC22 group, and-0.003 and -0.063 log(10) IU/mL in the PBO group, respectively (ITT population). Three out of ten patients with baseline HBsAg levels <= 100 IU/mL in the 1.0 mg/kg group obtained on-treatment HBsAg loss. Most AEs were mild (97.9%). There were no study drug-related serious AEs in the 1.0 mg/kg ASC22 group. Conclusions: Subcutaneous administration of 1.0 mg/kg ASC22 Q2W for 24 weeks was shown to be safe and well tolerated in virally suppressed CHB patients on NAs and can induce HBsAg decline, especially in patients with HBsAg <= 100 IU/mL.