The size of amorphous spherical aluminum phosphate particles was controlled by using urea and isopropylamine (IPA), and their texture was investigated by various means. The mean particle diameter (D-p) of the particles decreased with increasing urea concentration due to an acceleration in the precipitation reaction from decomposition of urea at elevated temperatures. The D-p decreased upon addition of IPA concentrations of up to 6 mol% to Al ions under a constant urea concentration, while D-p increased above this concentration because IPA produced electrolytes by reacting with HNO3; the electrolytes may reduce the range of Coulombic repulsion between charged primary particles. All the particles adsorbed selectively H2O molecules. IPA does not act as a template but operates as an effective additive for controlling particle size without altering the inner texture of spherical aluminum phosphate particles.