This study investigates the effect of wollastonite on the hydration and properties of magnesium potassium phosphate (MKP) cements. In MKP cements some efflorescence can occur; the presence of wollastonite suppresses efflorescence as the formation of Mg₂KH(PO₄)₂·15H₂O is prevented. The presence of wollastonite leads also to more heat (per g of MKP cement) due to the filler effect and due to the reaction of wollastonite, which increases strength, especially at low water-to-binder (w/b) ratio of 0.25 and at later ages, and lowers the pH values in the cement pore solution. The reaction of wollastonite does not lead to the formation of crystalline hydrates, both experimental and thermodynamic findings suggest the formation of amorphous hydroxyapatite and magnesium silicate hydrates (M-S-H).