Background: Access to primary healthcare is crucial for the delivery of Kenya’s universal health coverage policy. However, disparities in healthcare have proved to be the biggest challenge for implementing primary care in poor-urban resource settings. In this study, we assessed the level of access to primary healthcare services and associated factors in urban slums in Nairobi-Kenya. Methods: The data were drawn from the Lown scholars’ study of 300 randomly selected households in Viwandani slums (Nairobi, Kenya), between June and July 2018. Access to primary care was measured using Penchansky and Thomas’ model. Access index was constructed using principal component analysis and recoded into tertiles with categories labeled as poor, moderate and highest. Generalized ordinal logistic regression analysis was used to determine the factors associated with access to primary care. The adjusted odds ratios and 95 percent confident intervals were used to interpret the strength of associations. Results : The odds of being in the lowest versus combined moderate and highest access tertile were significantly higher for female than male-headed households (AOR 1.91 [95% CI 1.03-3.54]; p < .05). Households with an average quarterly out-of-pocket healthcare expenditure of ≥$30 had significantly lower odds of being in the lowest versus combined moderate and highest access tertile compared to those spending ≤ $5 quarterly (AOR 0.33 [95% CI 0.50-1.90]; p< .001). Households that sought care from private facilities had significantly higher odds of being in the lowest versus combined moderate and highest access compared to the public facilities (AOR 3.77 [95% CI 2.16-6.56]; p < .05). Conclusion : In Nairobi slums in Kenya, the gender of the household head, out of pocket healthcare expenditure, and source of primary care are significantly associated with access to primary care. Therefore, the universal health coverage program in this setting should be designed with an equity lens so that the most vulnerable groups within the community can have access.