2-Amino-1,3-selenazine template derivatives in the form of hydrobromides were synthesized. Phenyl, para-isopropylphenyl, and para-fluorophenyl were used as substituents. The distribution coefficients of the compounds in two-component systems modeling biological membranes, pH 2.0 and 7.4 buffer solution-organic solvent, were determined by a shake-flask method within the temperature range of 293 K to 313 K. Influences of the molecular structure, pKa, and pH of the buffer solutions, temperature, and solvent chemical nature on the distribution processes were investigated. Distribution thermodynamic functions were calculated for the selenazines under 298 K. It was established that the selenazines studied are substances with high membrane permeability.