The onset of thermosolutal convection during upwards solidification of a binary melt is investiga-ted by using linear stability theory. The present study concerns the stabilizing effect of temperature on the onset of thermosolutal convection. The results show that the critical solutal Rayleigh number increases with increasing the thermal Rayleigh number. This reflects the fact that an increase in thermal Rayleigh number makes the system more stable, while the system becomes more unstable with an increase in Lewis number or schmidt number. Multicell convection is exhibited at onset condition and this thermosolutal convec-tion is confined mainly to the vicinity of the interface. With increasing the thermal Rayleigh number, this trend becomes more pronounced with multicell patterns more distinguished.