Abstract: The crankshaft is an important component of an I.C engine. This converts the reciprocating displacement of the piston in to a rotary motion of the crank. An attempt is made in this paper on a single cylinder 4-stroke I.C engine. The 3-d modelling of the crankshaft and the analysis is to done by using CATIA-V5 software. And applying the boundary conditions on the crankshaft. The modal analysis is to be done in two cases i.e free-frequency and frequency analysis. Then the results are in free frequency analysis the resonance frequency is 1150.967Hz occurred at the 7th node. In frequency case minimum frequency occurred at the fillet areas is 890.735Hz maximum frequency is 5539.023Hz.