Although a significant amount of work has already been devoted to the prediction of as-cast grain size in inoculated aluminum alloys, most models treated the grains either spherical or directly dendritic. The influence of morphology transition from spherical to dendritic and subsequent dendritic grain growth has not been investigated and discussed in detail, especially in non-isothermal melt solidification condition (without recalescence). In this work, we propose a new grain size prediction model in which the morphology transition and dendritic growth are considered. A comparison has been made between forced spherical growth model and the one taking into account the morphology transition and dendritic growth. It is demonstrated that spherical growth is an acceptable approximation for well grain refined aluminum alloys in both isothermal and non-isothermal melt solidification. The difference in the predicted grain sizes based on the two different grain growth models is small. However, for not well grain refined aluminum alloys, e.g. low inoculation addition level or/and at low cooling rate condition, the dendritic grain growth model has a more significant influence on the predicted grain size and it is important to take it into consideration.