Antimonene, a new elemental two-dimensional (2D) material, attracts extensive attention recently. In particular, such 2D structure has been successfully fabricated by various strategies experimentally (Nat. Commun. 7 (2016) 13352; Adv. Mater. 28 (2016) 6332-6336; Angew. Chem. Int. Ed. 55 (2016) 14345-14349; Nano Lett. 17 (2017) 4970-4975). In this report, we, using first-principles calculations based on density functional theory (DFT), studied the effects of interstitial dopings of 3d transition metal (TM) atoms on antimonene. Our calculations revealed that the geometric structure of antimonene can be well kept after dopings of the TM atoms. Due to the relatively large values of the binding energies, TM atoms can robustly occupy at the interstitial site of antimonene. Interestingly, we found interstitial doping can make nonmagnetic antimonene system exhibit novel magnetic behavior. Moreover, interstitial doping also can effectively functionalize the electronic property of antimonene that antimonene system can be a half-metal, metal or spin-polarized semiconductor depending on the kind of impure atoms. In addition, the effect of doping of two TM atoms on antimonene was also checked. It was found that TM atoms prefer to dope at the adjacent sites due to the strong magnetic coupling, which associates with the new electronic and magnetic properties. All these results demonstrate that interstitial doping is a feasible method to tune the properties of antimonene, which is important for designing and developing new antimonene-based electronic devices.