CaSiO (CS) ceramic has been extensively studied for biomedical applications. The main advantages are its ability to induce bone-like apatite formation and the beneficial effects of the dissolution products on the bone cells, resulting from high reactivity of CS in liquid solutions. However, the high reactivity also results in a rapid degradation rate and accordingly leads to a high pH value in the body fluid, adversely affecting bone cell responses, especially when CS is used as a highly porous scaffold. In this study, we provide an approach to minimize this pH-dependent cell damage and maximize the beneficial effects of the dissolution products of the CS scaffold by adding chemically stable and biocompatible Zn-containing hardystonite (CaZnSiO, HT) into the CS scaffold, the resultant composite scaffold is referred to as HT-CS. We investigated the responses of primary human osteoblasts (HOBs) to the CS, HT and the HT-CS scaffolds. HOBs on HT and HT-CS scaffolds attached better than on the CS scaffold. HOBs cultured on the HT-CS scaffolds expressed higher gene expression levels for Runx-2, osteopontin (OPN), osteocalcin (OCN), bone sialoprotein (BSP), and collagen type I (Col-I) and enhanced alkaline phosphatase (ALP) activity compared to those on the CS and HT scaffolds. The higher activity of the HOBs cultured on the HT-CS scaffold was ascribed to the moderate pH variation and the dissolution products containing Ca, Si and Zn.