Abstract- This paper offers a new weighted distribution called size biased weighted transmuted weibull distribution, denoted by (SBWTWD). Various useful statistical properties of this distribution are derived in this paper such as, the cumulative distribution function, Reliability function, hazard rate, reversed hazard rate and the rth moment. Plots for the probability density function at different values of shape parameters are provided. The maximum likelihood estimators of the unknown parameters of the proposed distribution are obtained. One data set has been analyzed for illustrative purposes.