In this work, we firstly prepared new sealed graphene capsules (GCs) that were about 300 nm in size and had different morphologies using a simple reduction method. The quality of the graphene oxide (GO) sheets and the concentration of hydrazine hydrate are proposed to be influencing factors for the formation of sealed graphene capsules. GCs are covalently functionalized with 5,10,15,20-tetra-(4-aminophenyl)porphyrin, forming dispersible GC–aminoporphyrins in aqueous solution. The observed fluorescence quenching of the GCs by the aminoporphyrin indicated that the GCs are electron donors and electron transfer occurs from the GCs to the aminoporphyrin. This Förster Resonance Energy Transfer (FRET) between the GCs and aminoporphyrins is probably the reason for the enhancement of ¹O₂ generation of the GC–aminoporphyrins. More importantly, the as-prepared GC–aminoporphyrin nanohybrids as novel photosensitizers (PSs) with a short excitation wavelength can be used as PDT reagents for the treatment of malignant melanoma A375 with high efficiency. We expect that GC–aminoporphyrins will be promising PSs in future cancer therapy.