Microcrystals of (E)-8-(3,4-dimethoxystyryl)-1,3-diethyl-7-methyl-3,7-dihydro-1H-purine-2,- 6-dione having an average particle size of less than 50 .mu.m; microcrystals of (E)-8-(3,4-dimethoxystyryl)-1,3-diethyl-7-methyl-3,7-dihydro-1H-purine-2,- 6-dione having an average particle size of less than 50 .mu.m and a crystallinity of 20% or more or the like, which possess excellent solubility, stability, bioavailability, dispersing property in a pharmaceutical formulation; and the like are provided. A solid pharmaceutical formulation which is characterized by comprising the same is also provided.