Pension schemes in Kenya provide income for individuals who attain the retirement age and consequently boost economic growth as well as accelerate domestic savings. The industry is regulated by the Retirement Benefits Authority (RBA). The purpose of the study was to determine the relationship between operational practices on cost efficiency in defined contributions pension schemes in Kenya. The specific objectives were to determine the relationship between service provider costs on cost efficiency in defined contributions pension schemes, to examine the relationship between fund size on cost efficiency in defined contributions pension schemes, to determine the relationship between portfolios mix on cost efficiency in defined contributions pension schemes and to examine the relationship between investment strategy on cost efficiency in defined contributions pension schemes. The study will be significant to the management of defined contributions pension schemes in Kenya and other researchers. The study adopted a descriptive research design. The target population was all the 1,262 pension schemes in Kenya. Stratified random sampling was employed to select small schemes, medium schemes, large schemes and mega pension schemes in Kenya and obtained a total of 304 sample population. The study used secondary data. Descriptive statistics was performed by getting frequencies, means, and standard deviation for the purpose of understanding the results, which was displayed in tables, charts, and graphs. A multiple regression model was fitted to the data and the results revealed that there was a relationship between cost efficiency and service provision expenses, portfolio mix, fund size and investment strategies. Service provision expenses for a pension scheme should be able to cover the cost of administration without unduly compromising the growth of pension savings. Further, while a substantial fund size offered advantages, it should be complemented by strategic acumen and diligent oversight to ensure the scheme delivers on its mandate. A balanced and diversified portfolio is considered a cornerstone providing a buffer against market volatility and therefore enhancing the prospects of sustainable goals and cost efficiency. Finally, the cost associated with portfolio mix and risk management was a necessary investment in securing the long-term sustainability and stability of the pension fund. Recommendation for further studies on cost efficiency of defined benefits schemes should be done as well as further studies on challenges facing pension schemes in Kenya