The advent of immune checkpoint inhibitors (ICIs) has revolutionized the treatment landscape for extensive-stage small cell lung cancer (ES-SCLC) patients. However, many patients eventually develop resistance to immunotherapy. While continued ICI therapy beyond disease progression has shown survival benefits in various cancers, research specific to ES-SCLC remains limited. Our study aimed to further evaluate the efficacy and safety of atezolizumab continuation therapy to optimize the ICI continuation strategies for ES-SCLC. In this multicenter study, all enrolled patients received continued atezolizumab in combination therapy as second-line (2L) treatment after progression of first-line (1L) chemo-immunotherapy. The efficacy was measured by median overall survival (mOS) and median progression-free survival (mPFS). Safety was evaluated based on incidence of adverse events (AEs). Among the 28 eligible patients in this study, mPFS was 4.07 months [95% CI: 1.15 to 6.98], and mOS was 18.87 months [95% CI: 15.28 to 22.45]. In the safety analysis, respiratory-related AEs were the most common, including cough (35.7%), dyspnea (35.7%), pneumonitis (35.7%). Additionally, thyroiditis (17.9%) was the most generally reported immune-related adverse events (irAEs). In subgroup analysis, the LTR group (1L-PFS >= 6 months) showed longer mOS compared with the STR group (1L-PFS < 6 months) [19.98 vs. 8.68 months, p = 0.021]. Patients with greater DpR (>= 29% than < 29%) had longer mOS: 21.84 vs. 14.63, p < 0.01]. Atezolizumab continuation therapy demonstrated promising efficacy and manageable safety in ES-SCLC patients progressing after 1L chemo-immunotherapy, particularly in those with favorable 1L treatment responses.