Drawing on social exchange theory and attribution theory, this study explores whether newcomers’ helping behavior benefits their adjustment and whether the helping behavior attributed by coworkers to certain motives (prosocial motivation and impression management motivation) moderates these benefits. On the basis of results obtained from time-lagged surveys conducted with 114 newcomers, the study suggests that newcomers’ helping behavior positively influences newcomers’ distal outcome (i.e., organizational commitment) through the mediating effects of two proximal outcomes (task mastery and social integration). We also find that the benefits of newcomers’ helping behavior to their proximal adjustment outcomes are stronger when coworkers attributed newcomers’ helping behavior to prosocial motives but are not influenced by the attribution to impression management motivation. This study (1) theorizes and provides preliminary evidence for the positive implications of newcomer helping behavior on newcomers’ subsequent work performance and social integration and (2) provides evidence that two types of attribution are independent and have distinct moderating effects.