Today, Information security becomes one significant need that concert with crypthographic applicatin for managing confidentiality, integrity, autentication and non repudiation services. Random number generator as the heart of a security system could be a very potential target for adversary to reduce the security. Attack on random generator through insertion, deletion, modification, or even destruction attacks. In insertion attack, it could be achieved by reducing or vanishing the random property of the output sequences which is the most absolute requirement in a security system using crytographic application. In trying to figure out the effect of insertion attack on random property of the output sequences of a random number generator. The writer did a research by mounting 1-bit insertion attack on 5000 sample random sequences in 5-level of insertion block ( 64, 128, 256, 512 and 1024 bit). The random property is achieved by using DieHard test tool with significant level of a= 0,01. All 1000 random sequences produced by Mother of All Random Number Generators that will is tested by DieHard battery to assure the random property. The insertion bit sequence is generated by KISS Generator that will be inserted in random manner based on another random sequence produced by the same generator using different seed. The experiment results showed that with significant level of a= 0,01, the sequences that loss the random property is in the range of 1,2% and 2,8% that is higher than error tolerance of 1%. If we use higher a= 0,05, we found that the random sequences that loss their random property would be in the range of 6,2% and 9,6% which is beyond the tolerance of 5% error. Based on the results, we could conclude that insertion attack on random generator is a potential threat that could not be disobeyed. Keywords: PBA/PBPA, Insertion Attack, Randomness, Error Tolerance