In　this　paper,　a　third-order　waveguide　bandpass　filter　(BPF)　based　on　slotted　spherical　resonators　with　a　wide　spurious-free　stopband　is　presented.　The　resonator　consists　of　a　spherical　cavity　with　slots　opened　at　the　top　and　bottom.　Compared　with　a　non-slotted　spherical　resonator,　the　slotted　resonator　suppresses　the　two　spurious　modes　(TM211　and　TE101)　whilst　maintaining　the　fundamental　TM101　mode.　The　unloaded　quality　factor　of　the　TM101　mode　is　not　significantly　degraded.　This　is　achieved　by　interrupting　surface　current　and　radiating　the　unwanted　spurious　modes　with　the　slots.　The　BPF　is　designed　at　a　center　frequency　of　10　GHz　with　a　fractional　bandwidth　of　1%.　Two　filter　prototypes　are　fabricated,　one　using　metal-based　selective　laser　melting　(SLM)　and　the　other　by　polymer-based　stereolithography　apparatus　(SLA)　techniques.　The　slots　also　facilitate　the　copper　electroplating　process　for　the　SLA-printed　filter.　The　measured　results　show　that　the　average　passband　insertion　losses　of　the　SLM-　and　SLA-printed　filters　are　0.33　and　0.2　dB,　respectively.　The　corresponding　passband　return　losses　are　better　than　22　and　20　dB.　The　filters　demonstrate　excellent　passband　performance　and　wide　spurious-free　stopbands　up　to　16　GHz　with　stopband　rejections　of　over　20　dB.