Effects of partial band jamming on the performance of generalized selection combining (GSC) Rake receiver in direct sequence spread spectrum (DS-SS) communications have been investigated. Especially, we focus on effects of jamming on optimum spreading bandwidth for a fixed complexity GSC Rake receiver. The received signals are considered to undergo multipath fading over an independently and identically distributed (i.i.d.) Rayleigh channel, Expressions for performance measure at jamming environment have been derived as a function of system parameters and signal to jamming power ratio (P/J). A flat power delay profile (PDP) is considered for DS-SS. The idea is extended to direct sequence ultra wideband (DS-UWB) communications considering an exponentially decaying PDP. A fixed complexity GSC receiver designed to perform optimally for a given system bandwidth by outputting minimum achievable BEP, is found to perform sub-optimally in presence of jamming in both cases. However, effects of jamming are much less pronounced in case of a decaying PDP.