A new "effective nuclei" concept for a simplified approach to the analysis of batch crystallization with agglomeration is proposed. The new effective-nuclei concept comes from agglomeration characteristics observed experimentally in a batch crystallizer Small-sized crystals could combine with both large-sized crystals and each other. Agglomeration among large-sized crystals can be neglected From these experimental results, new effective nuclei are defined as crystals at a size-boundary between small-sized crystals and large-sized crystals. By taking into account only large-sized crystals in formulating population balance equation, the agglomeration tetm can be omitted. The analytical solution of the population balance equation is induced for an ideal batch-cooling case (constant supersaturation and constant effective growth rate of crystal). The solution explains measured data well.