The evolution of initial droplet size distribution in clouds seeded and unseeded by flare particles and MP particles were investigated in MRI cloud simulation chamber. The experiments showed that hygroscopic flare seeding tended to further increase droplet concentrations, which is consistent with numerical simulation results (Kuba and Murakami, 2012). On the other hand, MP seeding did not show any significant change in droplet number concentration, being not consistent with numerical simulation results. In those experiments, MP with anti-caking agents was used because it is much easier to handle than pure MP. To reexamine the effectiveness of MP seeding and hopefully optimize the relative amount of anti-caking agents, we have revisited MP seeding experiments with and without anti-caking agents. As a result of cloud formation experiment using without anti-caking agents (pure NaCl) , approximately 100s after the onset of cloud formation, the number concentration of cloud droplets larger than 2 μm measured with both the CAS and Welas-OPC attained a peak value, which was almost the same as CN concentration. The number of cloud droplets larger than 10 μm has kept increasing for a while, and reached nearly 1,000 cm−3 at 300sec of elapsed time. For experiment of MP with anti-caking agents, the number concentration of cloud droplets larger than 20μm was less than in the case of pure NaCl, in spite of the similarities of the concentration of droplet smaller than 10 μm. It was an evidence that MP without anti-caking agents causes relatively more intensive broadening of the cloud droplet spectrum as compared to MP with anti-caking agents. The differences in seeding effects of MP with and without anti-caking agent on cloud droplet size distribution activated on background CCN ((NH4)2SO4) have been investigated to quantitatively understand. The size distribution of cloud droplets measured in the chamber experiments will be directly compared with those simulated by the detailed bin microphysics parcel model, which is based on the parcel model of Chen and Lamb (1994) and extended to implement the κ-Köhler theory (Yamashita et al, 2011).