We describe a microfluidic platform for solid phase screening using extremely small quantities of raw materials. On the basis of our previous setup for solubility measurement that generates saturated solutions directly from powder, the platform requires no solution in excess of that used for the droplet-crystallization experiment. The setup is compatible with most solvents and molecules without using surfactant. Using this microfluidic platform, we first measured the solubility of sulfathiazole in water, isopropanol, and acetonitrile. Second, we performed a polymorph screening of sulfathiazole using as little as 30 mg of raw material, for numerous identical cooling crystallization experiments from 80 to 10 °C. In the experiments presented, we obtained the three usual polymorphs of sulfathiazole. We show that this economical approach yields reliable information on the probability of nucleation of a given polymorph, which is useful in pharmaceutical development.