To retrospectively evaluate the efficacy and safety of rituximab (Rtx) treatment in patients with anti-synthetase syndrome (ASS) and severe interstitial lung disease (ILD). Patients with severe ILD and >12 months follow-up post-Rtx were identified from the Oslo University Hospital ASS cohort (n = 112). Clinical data, including pulmonary function tests (PFTs), were retrospectively collected from medical reports. Extent of ILD pre-, and post-Rtx was scored on thin-section high-resolution CT (HRCT) images and expressed as a percentage of total lung volume. Muscle strength was evaluated by manual muscle testing of eight muscle groups (MMT8). Altogether, 34/112 ASS patients had received Rtx; 24/34 had severe ILD and >12 months follow-up post-Rtx (median 52 months). In these 24 patients, the median percentage of predicted forced vital capacity, forced expiratory volume in 1 s (FEV1) and diffusing capacity of the lungs for carbon monoxide (DLCO) increased by 24%, 22% and 17%, respectively, post-Rtx. Seven patients (all with disease duration <12 months and/or acute onset/exacerbation of ILD) had >30% improvement in all three PFTs. HRCT analysis showed a median 34% reduction in ILD extent post-Rtx. MMT8 score increased post-Rtx. During follow-up, 7/34 (21%) Rtx-treated ASS patients died; 6/7 deaths were related to infections. The mortality rate in the Rtx-treated group was comparable to that of the remaining ASS cohort (25/78 deceased; 32%). This study, which included 24 Rtx-treated ASS patients with severe ILD, reports improved PFTs after a median 52 months follow-up post-Rtx. The best outcome was observed in patients with a disease duration <12 months and/or acute onset/exacerbation of ILD. The study indicates that Rtx could be a treatment option for selected ASS patients, but infections should be given attention.