Experimental work was conducted on oriented strand board webbed wood I-joists to investigate the buckling behavior. Both lateral buckling and local web buckling were witnessed in the tests. The two types of buckling were reproduced in the finite element simulations using ABAQUS. The buckling modes and usually overestimated buckling loads of a joist were obtained from linear eigenvalue buckling analysis. The buckling modes were then introduced into a joist as initial geometric imperfections to conduct nonlinear buckling analysis, and more reliable buckling loads were obtained. Based on statistics of the analytical results, the local web buckling capacity at a support was empirically expressed by the postbuckling load. The empirical formula was extended to local web buckling under a concentrated load applied to the upper flange, where a reduction in buckling load was made to take the effect of moment into account.