Family caregivers’ role in cancer and stroke care is overly burdensome. Studies have considered burden and predictors of burden but the influence of caregiving burden on health - promoting behaviours among cancer and stroke family caregivers in Nigeria is scarce. The purpose of this study was to determine the influence of caregivers’ perceptions of burden and health-promoting behaviours on informal caregivers of cancer/ stroke patients attending tertiary care facilities in South- South Nigeria. A descriptive cross-sectional survey was employed among 410 purposively selected cancer/ stroke patients’ family caregivers in tertiary care facilities, South- South Nigeria. A standardized Zarit burden interview scale and structured questionnaire were used to measure burden and determine health-promoting behaviours respectively. Descriptive (means, standard deviation and percentages) and inferential (ANOVA) statistics with a Fisher’s protected t- test at 0.05 level of significance were used for data analysis. The respondents experienced severe (F= 14.02; P= 0.810) burden in caregiving to cancer/ stroke patients. The influence of health- promoting behaviours (primary, secondary and tertiary preventions) among caregivers of cancer/ stroke is significantly high in the tertiary care facilities, South-South, Nigeria. Caregivers of cancer and stroke patients experienced severe levels of burden and health-promoting-behaviours in terms of prevention at the primary, secondary and tertiary activities were significantly high among respondents. This calls for knowledge mobilization and dissemination in Nigeria and beyond.