In the process of growing crystals in solutions, double diffusive convection due to thermal and solutal gradients occurs. A measurement system comprising a rapid heat-transfer control system and an accurate real-time phase-shifting interferometer has been developed to investigate the transient double diffusive convection. The heat-transfer control system has a small test-cell in which the liquid temperature is controlled by non-equilibrium thermoelectric devices. In-situ measurements of the transient double diffusive convection and crystal growth rates in aqueous solution are carried out by using this system. Transient double diffusive convection is observed directly and clearly. The crystal growth rates in the present experiments show a nearly constant value over the whole area of measured super saturation ratios. The reason for this phenomenon is considered to be the surface roughness induced by rapid cooling.