Neck strengthening for players in impact sports like rugby is receiving greater attention lately due to postulated associations with head and neck injury and concussion and while research is available on the effectiveness of neck strengthening interventions on professional rugby players, the same research has not been conducted on amateurs who make up the majority of rugby players. The aim of this study was to investigate the effectiveness of a 6-week neck strengthening intervention on a group of male amateur rugby union players (20.1 ± 2.0 yr, mean ± SD). In a randomized controlled trial, players worked with their trainer to practice neck-specific strengthening exercises 3 times per week for 6 weeks (strength group, n = 22) or performed no additional neck strengthening exercises (control group, n =17). Isometric maximal voluntary contraction (MVC) was measured pre and post the intervention in 4 different directions (flexion, extension, left and right lateral flexion). Compared to the control group the strength group improved neck strength in all directions except flexion (flexion 7.1 ± 13.0 kg, mean ± SD, 75/18/7%, chances of positive/trivial/negative increase in strength, p = 0.28; extension 13.5 ± 14.6 kg, 92/7/1%, p = 0.07; left lateral flexion 13.5 ± 11.3 kg, 97/3/0%, p = 0.02; right lateral flexion 13.8 ± 14.9 kg, 92/7/1%, p = 0.07. Our results indicate that a simple 6-week neck strengthening program improves isometric MVC strength in male amateur rugby players.