The purpose of the study was to examine the effects of students' conceptual understanding of chemical concepts and mathematical processing skills on algorithmic problem-solving skills. The sample (N = 554) included grades 9, 10, and 11 students in Turkey. Data were collected using the instrument "MPC Test" and with interviews. The MPC Test consists of 3 sections: 8 conceptual questions (Qcu), 8 algorithmic problems (Qcc), 8 mathematics questions (Qm). It was concluded that students' conceptual understanding and mathematical processing skills effected algorithmic problem-solving skills. The effects of conceptual understanding were much more than mathematical processing skills on algorithmic problem-solving skills. According to the MCT Test results, 10 students with high, average, and low grades were interviewed. Qualitative findings were consistent with quantitative results. There is a significant relationship between students' algorithmic skills and their mathematical skills. Also, it was concluded that students' conceptual understandings are effective on solving chemistry problems but solving chemistry problems correctly does not mean chemistry concepts can be understood truly and deeply on a molecular level. (Contains 3 tables and 2 figures.)