Solar energy is an appropriate alternative to replace fossil fuel. Making high efficient use of solar energy is a critical issue. As a kind of solar collecting medium, nanofluid shows excellent optical and photothermal conversion properties. In this work, lampblack ink, a type of traditional Chinese ink, was used as heat collecting medium for photothermal conversion. Two-step method was taken to prepared water-based lampblack ink nanofluids at mass fraction of 0.01%, 0.02%, 0.05%, 0.1% and 0.2% respectively. The thermal conductivity of lampblack ink nanofluid was mearsured. The transmission spectrum of lampblack ink nanofluid was tested by uv?vis-nir spectrophotometer. Extinction coefficient and solar weighted absorption fraction were also calculated. Dispersion stability of nanofluid was also considered. Photothermal conversion experiments were taken under solar simulator and natural sunlight. The results showed that lampblack ink nanofluids have better photothermal conversion performance than DI water. With increasing of mass fraction, photothermal conversion performance of lampblack ink nanofluid increased and then decreased. The maximum photothermal conversion efficiency could reach 76.7% under solar simulator, which was 26.4% higher than that of DI water. This work could provide new insights on the application of photothermal such as solar collectors for an effective and low-cost way to address the critical energy shortages challenges.