This paper presents analysis and modeling of the resonance effects in a monolithic microwave integrated circuit (MMIC) package using Finite Difference Time Domain method (FDTD). Objectives of the analysis are investigating and evaluating of the resonance effects in a stripline package, and predicting of the resonance parameters which are related to the physical dimensions of the signal line and the discontinuities. A broadband equivalent circuit model of two vies transition in a stripline package including the resonance effects is also developed and presented. Results of the analysis indicate that the package performance is very sensitive to the resonance effects due to the multiple reflections occurred on the signal line. Furthermore, the frequency response of the proposed equivalent circuit model is predicted and compared to the FDTD model of the package discontinuities. Good agreement has been obtained between both models over a wide frequency band. Equivalent circuit model presented in this paper greatly simplifies the analysis and simulation of a complex package including several transition discontinuities, where limits of the resonance effects can be predicted and modeled.