The Serb commander, Momir Nikolic, pleaded guilty in May to crimes against humanity for persecuting non-Serbs in Europe's worst atrocity since the second world war. In return for his plea, prosecutors dropped four other charges.
Nikolic, 48, was an assistant intelligence commander in the Bratunac Brigade which encircled the UN-declared "safe haven" of Srebrenica in eastern Bosnia.
Momir Nikolic listens as the judge
sentences him to 27 years in jail
Under the plea deal, prosecutors agreed to request a 15-20 year sentence and the defence said it would recommend 10 years.
But Judge Liu Daqun on Tuesday said neither term was sufficient, saying the massacre was "committed with a level of brutality and depravity not seen previously in conflict in former Yugoslavia".
Tribunal judges have found Serbs committed genocide in Srebrenica after overrunning it in summer 1995.
Bosnian Muslims tried
Another war crimes case has begun of two former Bosnian Muslim army commanders charged with atrocities during the 1990s Balkan wars.
Retired general Enver Hadzihasanovic, 53, and brigadier Amir Kubura, 39, have denied responsibility for murders of Croats and Serbs, many of them the prosecution says were killed by foreign Muslim fighters.
An estimated 200,000 died in the
1992-95 war - mostly Muslims
The commanders in the 3rd Corps of the Bosnia-Herzegovina army are accused of failing to prevent the cruel treatment and killing of detained Bosnian Croats and Serbs.
At least 200 Croats and Serb civilians were killed during Muslim attacks on Croat forces in central Bosnia between January 1993 and January 1994.
Prosecutors say captives were forced to dig trenches under fire or used as human shields.
The prosecution also says many of the crimes were committed by mujahidin who flocked from Muslim countries to fight alongside Bosnian Muslims during the bitter conflict in the former Yugoslavia.
Hadzihasanovic pleaded not guilty to seven counts of war crimes and Kubura to six counts before both were provisionally released in December 2001 before their trial.