ABSTRAK Telah dilakukan penelitian tentang pengaruh variasi asam boraks (H3BO3) pada sintesis katalis CuO melalui metode elektrodeposisi. Hasil karakterisasi XRD terhadap katalis A, C dan E menunjukkan ketiga katalis memiliki puncak serapan dominan CuO berfase tenorite dengan nilai d(A) masing-masing sebesar 2,52, 2,45 dan 2,46. Hasil penentuan ukuran partikel dengan menggunakan persamaan Debye-Scherrer pada ketiga katalis diperoleh informasi bahwa ukuran kristalin CuO pada katalis A, C dan E masing-masing sebesar 7,09 nm, 4,75 nm dan 5,72 nm. Penentuan morfologi terhadap CuO yang dihasilkan menggunakan SEM menunjukkan ketiga katalis berupa bongkahan dengan katalis A memiliki ukuran partikel katalis terkecil ±80 μm, sedangkan katalis E memiliki ukuran partikel katalis terbesar ±100 μm. Hasil penelitian menunjukkan bahwa katalis CuO dengan rasio mol CuSO4 dan H3BO3 sebesar 1 : 0,5 (katalis C) memiliki aktifitas katalis tertinggi dengan kemampuan degradasi pewarna metil biru sebesar 67,62% dan katalis CuO yang dihasilkan rasio mol CuSO4 dan H3BO3 sebesar 1 : 1 (katalis E) memiliki aktifitas katalis terendah dengan kemampuan degradasi pewarna metil biru sebesar 54,39%, sedangkan katalis CuO yang tanpa penambahan H3BO3 (katalis A) memiliki kemampuan degradasi pewarna metil biru sebesar 65,21%. Kata Kunci : Katalis CuO, Elektrodeposisi, Fotokatalitik, H3BO3. ABSTRACT The study on the effect variations of H3BO3 on CuO Synthesized using electrodeposition methods has been carried out succesfully. The results of physical characterization using XRD on the resulted CuO catalysts (A,C and E) shown that three catalysts have been a dominant absorption peaks as a CuO phased tenorite which the d(A) value are 2.52, 2.45 and 2.46, respectively. Particle size estimation by using the Debye-Scherrer equation on Synthesized CuO catalysts indicated that the particle size of A, C and E are 7.09 nm, 4,75 nm and 5.72 nm, respectively. Morphology characterization with employing SEM equipment shown that all catalysts have been taken agglomeration process, where as the CuO catalyst reffered as A has been the smallest particle size of 80 μm, approximately and the biggest size of particle found on CuO catalyst refered as E with its particle size is 100 μm approximately. Finally, Synthesized CuO indicated its catalytic activity on degradation of methylen blue dye. The results showed that the CuO catalyst with CuSO4 and H3BO3 mole ratio of 1: 0.5 (reffered as C ) has been the highest catalytic activity with degradation percentage of 67.62%, whereas the CuO catalyst prepared with mol rasio of CuSO4 : H3BO3 of 1: 1 ( referred as E) shown the lowest catalytic activity of 54.39%, however in case of CuO catalyst without dropping of H3BO3 in the sintisyzed proccess (reffered to A) shown its degradation ability is 65.21%. Keywords : CuO Catalyst, Electrodeposition, Photocatalytic, H3BO3.