Background: Primary care physicians (PCP) play an important role in detecting Familial Hypercholesterolaemia (FH) early. However, knowledge, awareness and practice (KAP) regarding FH among Malaysian PCP are not well established, and there was no validated tool to assess their FH KAP. Thus, the aim of this study was to adapt an FH KAP questionnaire and determine its validity and reliability among Malaysian PCP. Methods: This cross-sectional validation study involved Malaysian PCP with ≥ 1-year work experience in the primary care settings. In Phase 1, the original 19-item FH KAP questionnaire underwent content validation and adaptation by 7 experts. The questionnaire was then converted into an online survey instrument and was face validated by 10 PCP. In Phase 2, the adapted questionnaire was disseminated through e-mail to 1500 PCP. Data were collected on their KAP, demography, qualification and work experience. The construct validity was tested using known-groups validation method. The hypothesis was PCP holding postgraduate qualification (PCP-PG-Qual) would have better FH KAP compared with PCP without postgraduate qualification (PCP-noPG-Qual). Internal consistency reliability was calculated using Kuder Richardson formula-20 (KR-20) and test–retest reliability was tested on 26 PCP using kappa statistics. Results: During content validation and adaptation, 10 items remained unchanged, 8 items were modified, 1 item was moved to demography and 7 items were added. The adapted questionnaire consisted of 25 items (11 knowledge, 5 awareness and 9 practice items). A total of 130 out of 1500 PCP (response rate: 8.7%) completed the questionnaire. The mean percentage knowledge score was found to be significantly higher in PCP-PG-Qual compared with PCP-noPG-Qual (53.5, SD ± 13.9 vs. 35.9, SD ± 11.79), t(128) = 6.90, p < 0.001. The median percentage awareness score was found to be significantly higher in PCP-PG-Qual compared with PCP-noPG-Qual (15.4, IqR ± 23.08 vs. 7.7, IqR ± 15.38), p = 0.030. The mean percentage practice score was significantly higher in PCP-PG-Qual compared with PCP-noPG-Qual (69.2, SD ± 17.62 vs. 54.4, SD ± 19.28), t(128) = 3.79, p < 0.001. KR-20 value was 0.79 (moderate reliability) and average Kappa was 0.796 (substantial agreement). Conclusion: This study has proven that the 25-item adapted FH KAP questionnaire is valid and reliable. It can be used to measure and establish FH KAP among PCP in Malaysia.