Favorable though isotropic polymeric structures are in many applications, they are not optimized in some others. Janus particles, having two sides with completely different properties, are optimizing the use for these applications, from industrial emulsifiers to biomedicine. In this work, mushroom‐like Janus particles made of PS as the seed and PEA as the semispherical centers through (seeded) dispersion polymerization were synthesized. Afterward, the effects of the initiator, monomer, and stabilizer amount as well as polymerization temperature were studied. It is shown that, in the PS synthesis stage, an increase in polymerization temperature, initiator amount, and monomer amount, as well as a decrease in stabilizer amount, lead to an increase in particles' size and in PDI percentage. In addition, in the next stage, the synthesis of mushroom‐like particles with the PEA sites, an increase in initiator amount, monomer amount, and polymerization temperature, as well as a decrease in stabilizer amount lead to bigger PEA centers and in excessive amount. It is also shown that above the breakthrough, three‐part particles increase in number with the changes mentioned. It is concluded that with the determined optimized conditions in this work mushroom‐like Janus particles of PS/PEA can be synthesized.