Despite advances in the sphere of new drug synthesis, the synthesis of new substances with high biological activity remains an actual problem of modern chemistry. From the literature sources it is known that in many cases enhancement of biological activity is observed when going from thiosemicarbazones to the corresponding selenosemicarbazones. In the present research  2-formylpyridine 4-allylselenosemicarbazone acetic acid solvate (I) was synthesized and its crystal structure was determined by X-ray analysis. For substitution of sulfur atom by a selenium atom the starting 2-formylpyridine 4-allylthiosemicarbazone was alkylated with iodomethane and then  S-CH3 group was substituted by hydrogen selenide ion. The single crystals were obtained by recrystallization from chloroform solution with addition of acetic acid. The studied compound crystallizes in the orthorhombic space group Pbcn (a=7.957(2), b=17.066(1), c=22.260(1) Å,  α = β = γ = 90-, V=3022.8(3) Å3) (Fig. 1). The C=N-NH-C-Se core of I is planar within 0.029 Ǻ. The dihedral angle of 6-membered ring with mentioned backbone is equal to 2.5°.The C-H…O, NH…O and O-H…N hydrogen bonds link  I and solvent molecules into 1D-hydrogen-bonded chain along [010] direction (Fig. 2).