<![CDATA[This researct was aimed to develop and describe the validity of science process skills assessment instrument on the collision theory. This research used RD method. The assessment which has been developed use descriptive questions which considering the validity, reliability, and level of difficulty that measures the level of basic science process skills such as observe, communicate, predict, and inference. Based on the result of expert validation on content suitability, construction, and ability aspects, this assessment instrument was said valid with very high category. The results of teachers responses to the three aspects were very high category. Analysis items showed the assessment instrument have high validity, high level of reliability, and modest level of difficulty.Penelitian dan pengembangan ini bertujuan untuk mengembangkan dan mendeskripsikan validitas instrumen asesmen keterampilan proses sains pada materi teori tumbukan. Penelitian ini menggunakan metode RD. Asesmen berupa soal uraian dengan memperhatikan validitas, reliabilitas, dan tingkat kesukaran soal yang mengukur KPS tingkat dasar yaitu mengobservasi, mengomunikasikan, memprediksi, dan menginferensi. Berdasarkan hasil validasi ahli terhadap aspek kesesuaian isi, konstruk, dan keterbacaan, instrumen asesmen ini dinyatakan valid dengan kategori sangat tinggi. Hasil tanggapan guru terhadap ketiga aspek tersebut berkategori sangat tinggi. Analisis butir soal menunjukkan asesmen memiliki nilai validitas butir soal tinggi, reliabilitas tinggi, dan tingkat kesukaran soal sedang.Kata kunci: asesmen, keterampilan proses sains, teori tumbukan]]>
