It has been a requirement of this era to have the 21st century skills. Also, with the development of the technology, achievemet in life sciences and mathematics is being more significant every day. TIMSS, arranged to determine this achievement, contributes the improvement and development of education. Also it defines the success ranking among the countries. In this study, the relationship between the 21st century skill levels and the results obtained from TIMSS declared in 2015 and the effect of the education levels of parents of the students, the expactaions from educational life, taking private science courses were examined in terms of the impact on TIMSS science achievements. For this purpose, this study was completed with 418 students from three districs in İstanbul in 2018-2019 academic year selected by randomly sampling method. The normality distributions of data groups were examined by Kolmogorov-Smirnov and Shapiro-Wilk tests with the obtained data. The data were collected using TIMSS 2015 life sciences achievement test, demographic information of the students and 21st century skills scale. As a result of the analysis, it is determined that there is a statistically significant relationship between the science achievements of the students and parents’ education level, the expectation from educational life and taking private science course. No significant relationship is determined between TIMSS science achievement and 21st century skills.