We present a growth model with micro-foundations of a mixed health care system and physician dual-practice, to analyze for welfare-optimal government financing strategy for a mixed health system in developing countries. Calibrating the model for Indonesia, we find that a government subsidy to private health care is both growth- and welfare-enhancing, whereas it is more effective for the government to invest in health infrastructure instead of a public-sector “rewarding” policy in raising government physicians’ wage if its goal is to improve physician effort in public practice. Indeed, for the “rewarding” policy, a dynamic trade-off in growth is found, which is not previously documented in the literature. We also find the model to produce two regimes with different welfare-optimal health financing (a “normal” regime and a low public-sector congestion regime). In the former, welfare-optimal health financing strategy appears to be promoting private health subsidy at the expense of public-sector physician wages. In the latter, the opposite is welfare-optimal.