The speciality of ranked set sampling is that it combines simple random sampling with other sources of information such as professional knowledge, auxiliary information, judgement, etc., which are inexpensive and easily obtained. In this study, the problem of estimating the unknown population mean of the study variable using information on auxiliary variable has been considered and new estimators have been developed with their properties in ranked set sampling and stratified ranked set sampling. Use of auxiliary information has been in practice for improving the efficiencies of the estimators of population parameters. Formulation of estimators for population mean using auxiliary information in ranked set sampling and stratified ranked set sampling has been main objective of the present investigation. Some empirical studies are also given in the support of theoretical findings.