The former St Helens and Great Britain half-back, who was also fined £300, will miss Friday's home game against Bradford and next week's trip to Catalan Dragons, after being sent off by referee James Child towards the end of Hull's 20-18 home defeat by Castleford last Friday for apparent use of the elbow.
It could have been worse for Long because he was initially charged with a grade D offence of intentional striking, which carries a ban of between three and five matches. However, that was downgraded to a grade C offence before his appearance in front of the Rugby Football League's disciplinary panel on Thursday.
It means Long, who also suffered concussion before being sent off against Castleford, will be available for Hull's Good Friday derby with Hull KR at the KC Stadium.
"I was proud of my record of having never been sent off in 17 years of playing professional rugby and I'm sad that's gone," Long said.
"I apologise for what happened. I was a bit concussed after a hit and my timing was off."