Background Despite improvements, adolescent fertility remains high in Africa. In Guinea, high fertility among adolescents and young women in urban areas remains a public health concern. This study aims to describe levels and trends in, and factors associated with using modern family planning (FP) methods among urban adolescents and young women in Guinea.Methods We used four Guinea Demographic and Health Surveys (DHS) conducted in 1999, 2005, 2012, and 2018. Among urban adolescents and young women (15–24 years), we examined trends over time in four key indicators: 1. Contraceptive use (% using any using any FP method among all and among those in need for FP), 2. Unmet need for FP (% not using any FP method among all and among those in need for FP) and 3.Modern contraceptive use (% of using modern FP methods and among those in need of FP), and 4. % using modern FP method (demand satisfied). We multivariable logistic regression to examine association between socio-demographic factors and modern FP use (indicator 2) on the most recent DHS dataset (2018).Results We found a statistically significant changes over the time period exmained in modern contracetive use (8.4% in 1999 to 12.8% in 2018, p < 0.01), demand satisfied (29.0% in 1999, 54.1% in 2018, p < 0.001), and halving of unmet need for FP (from 15.8% in 1999 to 8.6% in 2018, p < 0.001). The most important changes in these two indicators occurred between 1999 and 2005.. Compared to those 15–19 years, young women (20–24) more likely to use modern FP methods. Those living in Faranah and Kankan more likely to use modern FP method than those in Conakry. Middle and richer wealth quintile households were more likely to use modern FP compared to poorer. Married women compared to nevever married and those from the Peulh and Malinke ethnic groups compared to Soussou were less likely to use modern FP methods.Conclusion Despite some progress, efforts are still needed to improve FP method use among urban adolescent and you women. Future policies and intervention programs should emphasize on improving adolescents’ reproductive health knowledge and increasing awareness of FP method use. The focus should also be on adolescents aged 15–19 years, disparities of urban administrative regions, ethnic groups, and wealth index, especially the poor quintiles.