The conversion of newly developed three dimensionally printed calcium sulfate hemihydrate (70–90% wt/wt CaSO4·0.5·H2O) based materials to calcium phosphate bioceramics by phosphorization in di-sodium hydrogen phosphate solution at 80°C for 4, 8, 16 and 24 h was studied. It was found that transformation rate, phase composition and mechanical properties were influenced by porosity in the fabricated samples and by the duration of the phosphorization treatment. Formulation with 85% CaSO4·0.5 H2O showed the fastest transformation rate and resulted in the highest flexural modulus and strength. Depending on the materials formulation, XRD, FT-IR and EDS revealed that calcium deficient hydroxyapatite (CDHA) or a mixture of CDHA and dicalcium phosphate anhydrous (DCPA) were the resulting phases in the transformed samples. After cell culturing for 14 and 21 days, human osteoblast cells were observed to attach to and attain normal morphology on the surface of the transformed sample containing 85% CaSO4·0.5 H2O. Various sizes and shapes of mineralized nodules were also found after 21 days.