An injectable in situ-forming gel (ISG) is a promising approach as a drug delivery system. In this study, natural resins including aloe, benzoin and propolis dissolved in N-methyl pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) were investigated as ISG systems for their ability to form matrices in phosphate buffer. Regarding their functions as ISG, their pH values, viscosities, flow behaviours, surface tensions and injectabilities were tested. Benzoin and propolis exhibited greater matrix formation than aloe, owing to their higher resin contents. Benzoin and propolis in DMSO formed matrices with a faster solvent exchange rate compared with those in NMP. The former had a higher viscosity than the latter, but both of them exhibited similar densities and surface tensions. The 35% and 40% w/w benzoin in DMSO exhibited dominant matrix formations with acceptable injectability via syringe. The 35% w/w benzoin and propolis ISG in DMSO efficiently inhibited the growth of Staphylococcus aureus strains, and the propolis ISG also exhibited a clear inhibition zone against Porphyromonas gingivalis, whereas aloe did not. From the cell viability assay, propolis exhibited a higher toxicity against HCT116 colon cancer cells (IC50=95 µg/ml) compared with benzoin (IC50=400 µg/ml), whereas the resin from aloe showed no toxic effect on this cell. Due to their rapid insoluble matrix formation after contacting aqueous fluid as well as their antibacterial and cytotoxic activities against colon cancer cell, the 35% w/w benzoin and propolis in DMSO have the potential for use as a matrix former for ISGs.