<![CDATA[This research was aimed to describe the validity of knowledge assessment instrument on Bohrs atomic theory and quantum mechanics atomic theory topic. This assessment instrument used multiple choice form test which considering the reliability, validity, level of difficulty, discrimination power, distractors power, sensitivity, and practicability by teachers and students responses. The RD method was used in this reseach. This assessment instrument was valid based on expert judgement on content suitability, readability, and construction aspects, and it was said practicable based on teachers and students responses where all aspects of it was categorized as high. The empirical testing showed that this assessment instrument have high level of reliability, modest validity, modest level of difficulty, high discrimination power, good distractors, and less sensitive.Penelitian ini bertujuan untuk mendeskripsikan validitas instrumen asesmen pengetahuan pada materi teori atom Bohr dan mekanika kuantum. Asesmen berupa soal pilihan jamak dengan memperhatikan reliabilitas, validitas, tingkat kesukaran, daya beda, daya pengecoh dan sensitivitas soal, serta kepraktisan menurut respon guru dan siswa. Metode penelitian yang digunakan adalah metode RD. Instrumen asesmen ini dikatakan valid berdasarkan hasil validasi ahli terhadap aspek keterbacaan, konstruksi, dan kesesuaian soal dengan materi, dan instrumen asesmen dikatakan praktis berdasarkan respon guru dan siswa dimana semua aspek termasuk kategori tinggi. Uji empiris menunjukkan asesmen memiliki nilai reliabilitas tinggi, tingkat kesukaran soal sedang, daya beda soal tinggi, daya pengecoh opsi jawaban berfungsi baik, validitas butir sedang dan sensitivitas soal kurang sensitif.Kata kunci: instrumen asesmen, reliabilitas, teori atom bohr dan mekanika kuantum]]>
