Introduction: Adherence towards childhood immunization (completeness and timeliness), with consideration of age-dependent-seroconversion, is the basis for children protection. Despite high global and national immunization coverage, vaccine preventable diseases' are rising. This study aimed to determine adherence (completeness and timeliness) towards different vaccines of childhood immunization and associated factors among mothers of under five children. Methods: Cross-sectional study design was conducted at a health clinic in Seremban. Total of 320 mothers of under five children attending child health clinic selected via systematic random sampling. Data collection was via validated self-administered questionnaires and proforma, analysed using SPSS version 22. Associations between categorical variables determined by chi-square tests. Results: Consented respondents were 314; resulting in response rate of 98.1%. Adherence (completeness) was 98.09% but only 56.5% - 97.1% of respondents adhered in terms of timeliness. Types of transportation was significantly associated with adherence (completeness), p=0.041. Employment status was significantly associated with adherence (timeliness) towards BCG (p=0.008), Hepatitis B dose one (p=0.018) and dose two (p=0.040) vaccines. Education level was significantly associated with adherence (timeliness) towards DTaP/IPV/HiB dose four (p=0.019). Maternal age and usage of government clinic were significantly associated with adherence (timeliness) of MMR dose one, p=0.030 and p=0.017 respectively. Conclusion: Adherence (completeness) was high but varying adherence towards vaccine timeliness. Transportation types associated with completeness. Employment status associated with BCG, first and second doses of Hepatitis B vaccines' timeliness. Education level associated with fourth dose of DTaP/IPV/HiB. Maternal age and usage of government clinic associated with timeliness of first dose MMR.