Twenty dogs with canine atopic dermatitis (CAD) were treated with rush sublingual immunotherapy (SLIT), with a 48 hour build-up phase and 6 months maintenance phase (treated by antigen once every 3-4 weeks). The canine atopic dermatitis extent and severity index (CADESI)-4 was evaluated before treatment (baseline) and after 6 months. An open, non-controlled, non-randomized pilot trial was conducted to assess the effectiveness and safety of rush SLIT for environmental allergen extracts (Dematophagoides pteronyssinus and D.farinae mix and other). Three dogs dropped out and 17 dogs finished the trial. CADESI-4 at baseline was 60.6±27.1 (range 17-107, n=17). After 6 months of SLIT treatment, CADESI-4 was 37.4±36.0 (range 5-152, n=17) (p <0.01), which was a 38.3% reduction. A significant improvement, defined as a CADESI-4 reduction of > 30%, was observed in 13 out of 17 dogs (76%). A moderate improvement, defined as a CADESI-4 reduction of < = 30%, was observed in 2 dogs (12%). In the other 2 dogs (12%), CADESI-4 worsened or showed no change. However, no severe adverse effects were observed during the trial.Therefore, rush SLIT against environmental allergen extract for CAD showed effectiveness and safety as evidenced by the reduction of CADESI-4 after 6 months SLIT without severe adverse effects.