To provide a heat expandable microsphere excellent in heat resistance and high in expansion ratio and exhibiting stable expansion behavior.

There is provided a heat expandable microsphere of which outer shell containing a foaming agent is obtained by forming a copolymer having a polymethacrylimide structure from a mixture of polymerizable monomers containing a nitrile-based monomer containing methacrylonitrile (excluding one containing methacrylonitrile of 50 wt.% or less in the nitrile-based monomer) and a monomer having a carboxyl group containing methacrylic acid, and which has a b* value after heating at 240°C for 2 minutes of 100 or less.