Nuclear stress placement is a complex issue involving grammar, semantics, pragmatics, and information structure. This study examined the nuclear stress placement patterns in reading recordings produced by lower-intermediate and advanced adult EFL learners in China, and assessed the effects of explicit training on controlled production of nuclear stress. It was found that different types of nuclear stress presented asymmetrical difficulties to EFL learners. Production of some types showed more resistance to improvement, while others seemed more susceptible to explicit training, but with only short-term effects. Thus, EFL pronunciation teachers should give priority to those types of nuclear stress that are sensitive to explicit training and spend less time on those types that are either resistant to explicit training or that can be implicitly picked up by learners in the long run.