The prime purpose of this investigation was to improve Pre-service Chemistry Teachers (PCTs) understanding of reaction related concepts of Aliphatic Hydrocarbons (AHCs). Participants were 12 PCTs selected from a pool of 87 second year PCTs taking Introductory Organic Chemistry course in Arbaminch college of Teachers Education, Southern Nations, Nationalities and Peoples Regional State (SNNPRS), Ethiopia. The study was carried out in 2017 G.C. The selection of partakers was made on random basis. Case study method was employed in this in-depth investigation. The study was conducted in 7 weeks duration covering all concepts of AHCs. Conventional Instructional Approach (CIA) was employed in the Comparison Group (CG) and Conceptual Change Instructional Approach (CCIA) through the use Conceptual Change Texts (CCTs) was used in the Intervention Group (IG). A semi-structured interview was used for evaluating understanding of PCTs in relation to reactions of AHCs. To analyze the interview data, a framework analysis approach was followed. Analyses showed that the PCTs in IG had improved gaining of reaction related concepts of AHCs than those in CG. Participants in the IG reflected reduced Alternative Conceptions (ACs) and more Correct Conceptions (CoCs) than those in the CG. Reduced ACs and more CoCs from analyses of detailed recordings of PCTs responses confirmed enhanced understanding of reactions of AHCs in the IG.