A laboratory experiment was conducted to study the effects of Bio-assay of the economic mite; Tetranychus urticae Koch by the levels of static magnetic field forces. Completely randomized experiment with three replicates was designed. Similar groups of eggs of T. urticae were exposed to the odd numbers of magnets ; 1,3 and 5 units ( 0.14- 4.0 ml.t. ) and even numbers of magnets; 2,4 and 6 ( 2.6-4.24 ml.t.). Check was left without magnetizing. The observations included, egg hatchability percentage, incubation period, life cycle, longevity, life span, survivability, mean number of eggs/ female and sex ratio of the 1 " generation. Results showed that there was a linear negative relationship between the force of magnetic field and the percentage of egg hatchability. Hatching eggs were decreased from 100 % in the check to 90.3% in 6 magnet unit's treatment. Also mean number of eggs and longevity decreased from 4.0 eggs & 16.9 days to 2.3 eggs & 11.4 days; while incubation period and life cycle were prolonged depending on the number of magnet pieces from 7.0 & 15.7 days to 8.4 & 12.0 days, respectively of the above-mentioned magnets exposure.